Computer sound system. Computer sound system sound system PC. Study of the functions of the sound system PC

know:

Sound PC system. Composition of the PC sound system. Principle of operation and technical specifications of sound boards. Directions of improving the sound system. The principle of processing sound information. Specification of sound systems.
Methodical instructions
Sound PC System - A complex of software and hardware performing the following functions:

recording audio signals from external sources, such as a microphone or a tape recorder, by converting input analog audio signals into digital and subsequent storage on the hard disk;
play recorded audio data using an external speaker system or headphones (headphones);
playing audio CDs;
mixing (mixing) when recording or playing signals from multiple sources;
simultaneous recording and playback of sound signals (Full Duplex mode);
processing of sound signals: editing, combining or separating signal fragments, filtering, change its level;
processing of the sound signal in accordance with the volumetric (three-dimensional - 3D-sound) of the sound;
generation using musical instruments synthesizer, as well as human speech and other sounds;
managing the work of external electronic musical instruments through a special MIDI interface.

The PC sound system is structurally sound cards, or installed in the motherboard slot, or the other subsystem of the PC installed on the motherboard or the extension card. Separate sound system functional modules can be performed as childboards installed in the appropriate sound card connectors.

Figure 10 - PC Sound System Structure
The classic sound system, as shown in Fig. 5.1, contains:

recording and sound recording module;
synthesizer module;
interface module;
module Mixer;
acoustic system.

The first four modules are usually installed on the sound card. Moreover, there are sound cards without a synthesizer module or a digital sound recording / playback module. Each of the modules can be performed either as a separate chip, or to enter a multifunctional chip. Thus, the chipset of the audio system may contain both several and one microcircuit.

Constructive performances of the PC sound system undergo significant changes; There are motherboards with chipset installed on them for sound processing.

However, the purpose and function of the modules of the modern sound system (regardless of its design) do not change. When considering the functional modules of the sound card, it is customary to use the terms "Sound System PC" or "Sound Map
Questions for self-control:

PC sound system;
Composition of the PC sound system;
Principle of operation and technical characteristics of sound boards;
Directions of improving the sound system;
The principle of processing sound information;
Specification of sound systems.

Topic 6.2 Sound Information Processing Interface Module
The student must:
have a presentation:

about PC Sound System

know:

composition of the sound subsystem PC;
principle of operation of the recording and playback module;
principle of operation of the module of the synthesizer;
principle of operation of the interface module;
the principle of operation of the mixer module;
organization of the acoustic system.

Composition of the sound subsystem PC. Recording and playback module. Synthesizer module. Interface module. Module mixer. Principle of operation and technical specifications of acoustic systems. Software. Sound File Formats. Speech recognition tools.
Methodical instructions
Record and Play System Record Module Perform analog-to-digital and digital-to-digital conversion in sound data programming mode or transmitting them through DMA channels (Direct Memory Access - direct memory channel).

Sound recording is the saving of information about sound pressure fluctuations at the time of the recording. Currently, analog and digital signals are used to record and transmit information about sound. In other words, the beep can be represented in analog or digital form.

At the entry of the PC sound card in most cases, the beep is applied in analog form. Due to the fact that the PC operates only by digital signals, the analog signal must be transformed into digital. At the same time, the acoustic system installed at the output of the PC sound card perceives only analog electrical signals, so after processing the signal using the PC, the inverse conversion of the digital signal to the analog one is necessary.

Analog-digital conversion is an analog signal conversion into digital and consists of the following main steps: sampling, quantization and coding.

^ The pre-analog beep enters an analog filter that limits the signal frequency band.

The amplitude quantization is the measurement of the instantaneous values \u200b\u200bof the amplitude of the discrete signal in time and the transformation of it into the discrete time and amplitude. Figure 11 shows the quantization process by the level of an analog signal, and the instantaneous amplitude values \u200b\u200bare encoded by 3-bit numbers.

^ Figure 11 - Analog-Digital Sound Conversion Scheme
Coding is to convert to the digital code of the quantized signal. In this case, the accuracy of measuring during quantization depends on the number of category discharges.

^ Figure 12 - time sampling and quantization by the level of an analog range of quantization of the amplitude of the countdown.
Analog-to-digital conversion is carried out by a special electronic device - an analog-to-digital converter (ADC), in which the discrete signal counts are converted into a sequence of numbers. The resulting flow of digital data, i.e. The signal includes both useful and unwanted high-frequency interference, to filter which the digital data obtained is passed through a digital filter.

The digital-based transformation in the general case occurs in two stages, as shown in Figure 12. At the first stage, from the digital data stream using a digital-to-analog converter (DAC), the signal counts are separated from the sampling frequency. At the second stage, a continuous analog signal is generated from the discrete samples by smoothing (interpolation) using a low frequency filter, which suppresses the periodic components of the spectrum of the discrete signal.

To reduce the number of digital data required to represent a sound signal with a given quality, use compression (compression), which consists in reducing the number of samples and quantization levels or the number of bits per count.

^ Figure 13 - Digital Conversion Scheme
Such methods for encoding audio data using special coding devices allow you to reduce the amount of information flow to almost 20% of the initial one. The selection of the encoding method when recording audio information depends on the set of compression programs - codecs (coding-decoding) supplied with the sound card software or part of the operating system.

Performing the functions of analog-digital and digital signal transformations, the recording module and digital sound reproduction contains the ADC, DAC and control unit, which are usually integrated into one chip, also called the codec. The main characteristics of this module are: sampling frequency; type and discharge of ADC and DAC; method of encoding audio data; The ability to work in Full Duplex mode.

The sampling frequency determines the maximum frequency of the recorded or playable signal. To record and reproduce human speech, 6 is 8 kHz; music with low quality - 20 - 25 kHz; To ensure high-quality sound (audio drive), the discretization frequency should be at least 44 kHz. Almost all sound cards support recording and playing a stereo sound signal with a sampling frequency of 44.1 or 48 kHz.

^ The discharge of the ADC and the DAC determines the discharge of the digital signal representation (8, 16 or 18 bits).

Full Duplex (full duplex) - data transmission mode over a channel, according to which the sound system can simultaneously receive (write) and transmit (reproduce) audio data. However, not all sound cards support this mode in full, as they do not provide high sound quality with intensive data exchange. Such cards can be used to work with voice data in the Internet, for example, when conducting teleconferences, when high sound quality is required.

Synthesizer module

Effective sound system synthesizer allows you to generate almost any sounds, including the sound of real musical instruments. The principle of the synthesizer is illustrated in Figure 14.

Synthesis is the process of recreating the structure of the musical tone (notes). A sound signal of any musical instrument has several time phases. In Figure 15, and show the phases of the sound signal arising when the piano key is pressed. For each musical instrument, the view of the signal will be peculiar, but three phases can be distinguished: attack, support and attenuation. The combination of these phases is called an amplitude envelope, the form of which depends on the type of musical instrument. The duration of the attack for different musical instruments varies from units to several tens or even up to hundreds of milliseconds. In the phase, called support, the amplitude of the signal almost does not change, and the height of the musical tone is formed during support. The last phase, attenuation, corresponds to a plot of a fairly rapid decrease in the amplitude of the signal.

In modern synthesizers, the sound is created as follows. A digital device using one of the synthesis methods generates a so-called excitation signal with a given sound height (note), which must have spectral characteristics, as close to the characteristics of the imitated musical instrument in the support phase, as shown in Figure 15, b. Next, the excitation signal is fed to the filter, simulating the amplitude-frequency response of the real musical instrument. An amplitude envelope of the same tool is applied to another filter input. Next, the set of signals is processed in order to obtain special sound effects, for example, echo (reverb), choral performance (Ho-Rus). Next, a digitalog conversion and signal filtering are made using a low frequency filter (FNH).

Figure 15 - Principle of action of a modern synthesizer: A - Sound Signal Phases; 6 - synthesizer scheme
The main characteristics of the synthesizer module:

sound synthesis method;
memory size;
the ability to hardware signal processing to create sound effects;
polyphony - the maximum number of simultaneously reproducible sound elements.

The sound synthesis method used in the PC sound system determines not only the sound quality, but also the composition of the system. In practice, synthesizers generating sound using the following methods are installed on the sound cards.

Frequency Modulation Synthesis Synthesis (FM-Synthesis - FM-Synthesis) involves using for the generation of a musical instrument to generate two complex form generators. The carrier generator generates the main tone signal, the frequency-modulated signal of additional harmonics, overtones that determine the timbre of the sound tool. The envelope generator manages the amplitude of the resulting signal. The FM generator provides acceptable sound quality, has a low cost, but does not implement sound effects. In this regard, the audio cards using this method are not recommended in accordance with the RS99 standard.

Wave Table Synthesis - WT-Synthesis Sounds (WAVE Table Synthesis - WT-Synthesis) is made by using pre-digitized Samples of real musical instruments and other sounds stored in a special ROM made in the form of a memory chip or integrated in the WT generator memory chip. WT synthesizer provides high quality sound generation. This synthesis method is implemented in modern audio cards.

^ The amount of memory on the sound cards with the WT synthesizer may increase due to the installation of additional memory elements (ROM) for storing banks with tools.

Sound effects are formed using a special processor effect, which can be either an independent element (microcircuit), or integrate into the WT synthesizer. For the overwhelming majority of cards with WT-synthesis, the effects of reverb and chorus have become standard. Synthesis of sound based on physical modeling provides for the use of mathematical models of sound formation of real musical instruments for generating digital form and for further conversion to a beep with a DAC. Sound cards using the physical modeling method have not yet been widespread, since there is a powerful PC for their operation.

Interface module Provides data exchange between the sound system and other external and internal devices.

The PCI interface provides a wide bandwidth (for example, version 2.1 is more than 260 Mbps), which allows you to transmit audio data streams in parallel. Using the PCI bus allows you to improve the sound quality, providing signal-to-noise ratio over 90 dB. In addition, the PCI bus ensures the possibility of cooperative sound data processing, when the processing and data transmission tasks are distributed between the sound system and the CPU.

MIDI (Musical Instrument Digital Interface - Digital Musical Instrument Interface) is governed by a special standard containing specifications on the hardware interface: channel types, cables, ports, with which MIDI devices are connected one to another, as well as a description of the procedure for exchanging data - information exchange protocol between MIDI devices. In particular, using MIDI commands can be controlled by lighting equipment, video equipment in the process of performing a musical group on the scene. Devices with MIDI interface are connected sequentially by forming a kind of MIDI network that includes a controller - a control device, which can be used as a PC and a music key synthesizer, as well as driven devices (receivers), transmitting information to the controller for its request. The total length of the MIDI chain is not limited, but the maximum cable length between two MIDI devices should not exceed 15 meters.

Connecting a PC to the MIDI network is carried out using a special MIDI adapter, which has three MIDI ports: input, output and pass-through data transmission, as well as two connections for connecting the joysticks.

^ The audio card includes an interface for connecting the CD-ROM drives.

Module Mixer

The sound card mixer module performs:

switching (connection / disconnection) of sources and sound signals, as well as regulation of their level;
mixing (mixing) multiple audio signals and adjust the level of the result.

The main characteristics of the mixer module include:

the number of mixed signals on the playback channel;
control signal level in each mixed channel;
regulation of the level of the total signal;
output power amplifier;
the presence of connectors for connecting external and internal
receivers / sources of sound signals.

Sources and sound signal receivers are connected to the mixer module through external or internal connectors. External sound system connectors are usually located on the rear panel of the system unit housing: JoyStick / MIDI - to connect a joystick or MIDI adapter; Micin - for connecting the microphone; Linein - linear input to connect any sources of sound signals; Lineout - linear output to connect any sound signals; SPEAKER - to connect headphones (headphones) or passive speaker system.

Software management mixer is carried out either by Windows tools or using a mixer program supplied with a sound card software.

Compatibility of the audio system with one of the standards of sound cards means that the audio system will provide high-quality sound signals. Compatibility issues are especially important for DOS applications. Each of them contains a list of audio cards, to work with which the DOS application is oriented.

The Sound Blaster standard supports applications in the form of games for DOS, in which sound support is programmed with the orientation of the Sound Blaster Sound Maps.

^ Microsoft's Windows Sound System (WSS) Standard includes a sound card and software package focused mainly on a business application.

Acoustic system (AC) Immediately converts a sound electrical signal into acoustic oscillations and is the last link of the sound-reproducing path. The AC, as a rule, includes several audio speakers, each of which can have one or more speakers. The number of speakers in speakers depends on the number of components that make up the beep and forming separate audio channels.

As a rule, the principle of operation and the internal device of the sound columns of domestic and used in technical means of informatization in the composition of the acoustic system PC is practically not vary.

Basically, the AC for PC consists of two sound columns that provide a stereo signal playback. Usually, each column in the AC for PC has one speaker, however, two are used in expensive models: for high and low frequencies. At the same time, modern models of acoustic systems make it possible to reproduce the sound in almost a whole hearing frequency range due to the use of the special design of the column or loudspeakers.

To reproduce low and ultra-low frequencies with high quality in the AU, in addition to two speakers, the third sound unit is used - subwoofer, installed under the desktop. Such a three-component AC for PC consists of two so-called satellite speakers reproducing medium and high frequencies (from about 150 Hz to 20 kHz), and a subwoofer, which reproduces the frequency below 150 Hz.

A distinctive feature of the AC for PC is the possibility of presence of its own built-in power amplifier. The speaker with the built-in amplifier is called active. Passive AC amplifier has no.

The main advantage of the active speaker is to connect to the linear output of the sound card. The active AC power is carried out either from batteries (batteries), or from an electrical network via a special adapter, made in the form of a separate external unit or power module installed in the body of one of the columns.

The output power of the acoustic systems for the PC may vary in a wide range and depends on the technical characteristics of the amplifier and speakers. If the system is designed to sound computer games, sufficient power is 15-20 W per column for the mid-size room. If you need to ensure good audibility during a lecture or presentation in a large audience, it is possible to use one AU, having a power of up to 30 W per canal. With an increase in the power of the AU, its overall dimensions increase and cost increases.

^ The main characteristics of the AC: a band of reproducible frequencies, sensitivity, harmonic coefficient, power.

The frequency band (FrequencyResponse) is an amplitude-frequency dependence of the sound pressure, or the dependence of the sound pressure (sound force) from the frequency of the alternating voltage, summing up to the coil of the speaker. The frequency band perceived by the Human Eh is ranging from 20 to 20,000 Hz. Columns, as a rule, have a range limited in the low frequency range of 40 - 60 Hz. Solve the reproduction problem of low frequencies allows the use of a subwoofer.

The sensitivity of the audio column (sensitivity) is characterized by sound pressure, which it creates 1 m at a distance when the electrical signal is supplied with a power of 1 W. In accordance with the requirements of standards, the sensitivity is defined as the average sound pressure in a certain frequency band.

The higher the value of this characteristic, the better the speakers transmits the dynamic range of the music program. The difference between the "quiet" and the most "loud" sounds of modern phonograms 90 - 95 dB and more. The speakers with high sensitivity are well reproduced as quiet and loud sounds.

The harmonic coefficient (Total Harmonic Distortion - THD) estimates nonlinear distortions associated with the appearance of new spectral components in the output signal. The harmonic coefficient is normalized in several frequency bands. For example, for high-quality Hi-Fi ACs, this coefficient should not exceed: 1.5% in the frequency range 250 - 1000 Hz; 1.5% in the frequency range 1000 - 2000 Hz and 1.0% in the frequency range of 2000 - 6,300 Hz. The smaller the value of the harmonic coefficient, the better the AU.

Electrical power (Power Handling), which is withstanding the AC is one of the main characteristics. However, there is no direct relationship between the power and quality of sound playback. The maximum sound pressure depends on the sensitivity, and the power of the ash mainly determines its reliability.

Often, the PC packaging for PC indicates the peak power of an acoustic system, which does not always reflect the real power of the system, because it may exceed a nominal 10 times. Due to the significant difference in the physical processes occurring during the tests of the AC, the values \u200b\u200bof electrical capacities may differ several times. To compare the capacity of various speavers, it is necessary to know which power indicates the manufacturer of products and what kind of test methods it is defined.

Some Microsoft column models are connected to a sound card, but to the USB port. In this case, the sound comes on the speakers in digital form, and its decoding produces a small chipset installed in the columns.
Questions for self-control:

Composition of the sound subsystem PC;
Record and Play Module;
Synthesizer module;
Interface module;
Module Mixer;
Principle of operation and technical specifications of acoustic systems. Software;
Sound File Formats;
Speech recognition tools.

Practical work 8. Sound system PC
The student must:
have a presentation:

about PC Sound System

know:

principles of processing sound information;
composition of the sound subsystem PC;
the main characteristics of sound circuit boards

be able to:

connect and configure the sound subsystems of the PC;
record audio files.

Section 7. Print Information Output Devices
Topic 7.1 Printer
The student must:
have a presentation:

about devices Print information

know:

the principle of operation of device output devices for printing a matrix printer. Main components and features of operation, technical characteristics;
principle of operation of device output information on the printing printer printing main nodes and features of operation, specifications;
the principle of operation of information conclusions for printing a laser printer The main components and features of operation, specifications.

General characteristics of print output devices. Classification of printing devices. Shock-type printers: principle of operation, mechanical nodes, work features, specifications, operation rules. Basic modern models.

^ Inkjet printers: principle of operation, mechanical components, work features, specifications, operation rules. Basic modern models.

Laser printers: principle of operation, mechanical components, work features, specifications, operation rules. Basic modern models.
Methodical instructions
Printers - Data output devices from a computer that converts information ASCII codes into the graphical symbols corresponding to them and fix these characters on paper.

The classification of printers can be performed by a variety of features:

method of forming symbols (aligning and sign about synthesizing);
chroma (black and white and colored);
method forming strings (serial and parallel);
printing method (Sillar, line and page)
print speeds;
resolution.

Printers usually work in two modes: text and graphic.

When working in text mode The printer takes from the computer the characters codes that must be printed from the signs of the printer itself. Many manufacturers equip their printers with plenty of built-in fonts. These fonts are written in the ROM printer and read only from there.

To print text information, there are print modes that provide various quality:

draft printing (DRAFT);
typographical print quality (NLQ - Near Letter Quality);
print quality close to typographic (LQ - Letter Quality);
high quality mode (SQL - Super Letter Quality).

IN graphic mode The printer is sent to the codes that define the sequences and location of the points of the image.

By the method of applying images on paper, printers are divided into shock action printers, inkjet, photoelectronic and thermal.

The audio system of the PC in the form of a sound card appeared in 1989, significantly expanding the possibilities of the PC as a technical means of informatization.

Sound PC System- A complex of software and hardware performing the following functions:

· Recording sound signals from external sources, for example, microphone or tape recorder, by converting input analog audio signals into digital and subsequent storage on the hard disk;

· Play recorded audio data using an external speaker system or headphones (headphones);

· Play audio CDs;

· Mixing (mixing) when recording or playing signals from several sources;

· Simultaneous recording and playback of audio signals (mode Full Duplex);

· Sound signal processing: editing, combining or separating signal fragments, filtering, change of its level;

· Treatment of sound signal in accordance with volumetric algorithms (three-dimensional - 3D-Sound)sound;

· Generation using musical instruments synthesizer, as well as human speech and other sounds;

· Management of external electronic musical instruments through a special MIDI interface.

The PC sound system is structurally sound cards or installed in the motherboard slot, or the other subsystem of the PC integrated on the motherboard or the expansion card, as well as the recording and playback devices (acoustic system). Separate sound system functional modules can be performed as childboards installed in the appropriate sound card connectors.

The classic sound system, as shown in Fig. 4.23, contains:

Recording and sound recording module;

Synthesizer module;

Interface module;

Module Mixer;

Acoustic system.

Fig. 4.23. Structure of the PC sound system.

Constructive performances of the PC sound system undergo significant changes; There are motherboards with chipset installed on them for sound processing.

However, the purpose and function of the modules of the modern sound system (regardless of its design) do not change. When considering the sound card functional modules, it is customary to use the terms "PC Sound System" or "Sound Card".

The audio system of the PC in the form of a sound card appeared in 1989, significantly expanding the possibilities of the PC as a technical means of informatization.

PC sound system -software and hardware complex performing the following functions:

recording audio signals from external sources, such as a microphone or a tape recorder, by converting input analog audio signals into digital and subsequent storage on the hard disk;

play recorded audio data using an external speaker system or headphones (headphones);

playing audio CDs;

mixing (mixing) when recording or playing signals from multiple sources;

simultaneous recording and playback of audio signals (mode FULL Duplex);

processing of sound signals: editing, combining or separating signal fragments, filtering, change its level;

processing of the sound signal in accordance with the algorithms of volumetric (three-dimensional - 3 D.- Sound.) sound;

generation using musical instruments synthesizer, as well as human speech and other sounds;

managing the work of external electronic musical instruments through a special MIDI interface.

The classic sound system, as shown in Fig. 5.1, contains:

Recording and sound recording module;

synthesizer module;

interface module;

module Mixer;

acoustic system.

Constructive performances of the PC sound system undergo significant changes; There are motherboards with chipset installed on them for sound processing.

2. Record and Play Module

The recording and playback module of the audio system performs analog-digital and digital conversion in software transmission mode or transmission to DMA channels (Direct. Memory. Access - Channel direct memory access).

The sound is known is longitudinal waves freely distributing in air or other medium, so the beep sounds continuously in time and in space.

If when recording sounds, use a microphone that converts the electrical signal continuous in time into time in time, the electrical signal is obtained in analog form. Since the amplitude of the sound wave determines the volume of the sound, and its frequency is the height of the audio tone, the electrical signal should be proportional to the height of the sound, and its frequency must match the frequency of the oscillations of the sound pressure.

Analog-Digital Conversionit is the conversion of an analog signal into digital and consists of the following main steps: sampling, quantization and coding. The diagram of analog-digital conversion of the beep is presented in Fig. 5.2.

The pre-analog beep enters an analog filter that limits the signal frequency band.

Signal sampling is to select an analog signal sample with a given frequency and is determined by the sampling rate. Moreover, the discretization frequency should be at least twice the highest harmonic frequency (frequency component) of the source audio signal. Since a person is able to hear sounds in the frequency range from 20 Hz to 20 kHz, the maximum frequency of sampling of the source sound signal should be at least 40 kHz, i.e., the counts are required to carry out 40,000 times per second. In this regard, in most modern sound systems PC, the maximum frequency of sampling of the sound signal is 44.1 or 48 kHz.

The amplitude quantization is the measurement of the instantaneous values \u200b\u200bof the amplitude of the discrete signal in time and the transformation of it into the discrete time and amplitude. In fig. 5.3 shows the process of quantization by an analog signal level, and instantaneous amplitude values \u200b\u200bare encoded by 3-bit numbers.

Coding is to convert to the digital code of the quantized signal. In this case, the accuracy of measuring during quantization depends on the number of category discharges. If the values \u200b\u200bof amplitudes are recorded using binary numbers and set the length of the code word N.discharges, the number of possible values \u200b\u200bof the code words will be equal 2 N. . There can be the levels of quantization of the amplitude of the countdown. For example, if the value of the countdown amplitude is represented by a 16-bit code word, the maximum number of amplitude gradations (quantization levels) will be 2 16 \u003d 65 536. For an 8-bit view, respectively, we obtain 2 8 \u003d 256 amplitude graduations.

Analog-to-digital conversion is carried out by a special electronic device - analog-digital converttelem(ADC), in which discrete signal counts are converted into a sequence of numbers. The resulting flow of digital data, i.e. The signal includes both useful and unwanted high-frequency interference, to filter which the digital data obtained is passed through a digital filter.

Digid transformationin general, occurs in two stages, as shown in Fig. 5.4. At the first stage, from a digital data stream with a digital-to-analog converter (DAC), the signal counts are isolated from the sampling frequency. At the second stage, a continuous analog signal is generated from the discrete samples by smoothing (interpolation) using a low frequency filter, which suppresses the periodic components of the spectrum of the discrete signal.

To write and store the audio signal in digital form requires a large amount of disk space. For example, a stereo sound signal with a duration of 60 s, digitized with a sampling frequency of 44.1 kHz with a 16-bit quantization for storage requires about 10 MB on the hard drive.

To reduce the amount of digital data required to represent a sound signal with a given quality, use compression (compression), which consists in decreasing (the number of samples and quantization levels or the number of bits, I. holy on one countdown.

Such methods for encoding audio data using special coding devices allow you to reduce the amount of information flow to almost 20% of the initial one. The selection of the encoding method when recording audio information depends on the set of compression programs - codecs (coding-decoding) supplied with the sound card software or part of the operating system.

The discharge of the ADC and the DAC determines the discharge of the digital signal representation (8, 16 or 18 bits). The overwhelming majority of sound cards are equipped with 16-bit ADCs and DACs. Such sound maps are theoretically attributed to the Hi-Fi class, which must provide studio sound quality. Some sound cards are equipped with 20- and even 24-bit ADCs and dads, which significantly improves the quality of recording / playing sound.

FULL Duplex (Full duplex) - data transmission mode on a channel, according to which the sound system can simultaneously receive (write) and transmit (reproduce) audio data. However, not all sound cards support this mode in full, as they do not provide high sound quality with intensive data exchange. Such cards can be used to work with voice data in the Internet, for example, when conducting teleconferences, when high sound quality is required.

Rule 2. Before turning on the device to the network, see what is written on the rear wall of the device.

Check the voltage at the output of the autotransformer at idle before connecting the device to it.

Check the value of the supply voltage device in the process of making copies.

Having finished working, remove the plug of the autotransformer from the network. Do not leave the autotransformer under the voltage!

Rule 3. It is very important to take into account the requirements for installing the copier. Install the device is needed on a flat horizontal surface. The deviation from the horizontal position leads to the redistribution of toner and the carrier in the apparatus cartridge towards the slope. Accordingly, their stirring is hampered and the uniformity of the magnetic shaft of the toner is disturbed.

Laboratory work. Study of the principle of operation of sound processing devices

purpose of work

Examine the structural scheme of the sound system of the PC, which make up the sound system.

7.2 Proceedings:

1) Get acquainted with the structural scheme of the PC sound system.

2) study the main components (modules) of the sound system.

3) Get acquainted with the principle of the synthesizer module.

4) Get acquainted with the principle of operation of the interface module.

5) Get acquainted with the principle of the module of the mixer.

1) the topic, goal, work work;

2) the wording and description of the individual task;

7.4 Control questions

1) Name the main modules of the classical sound system.

2) What is the essence of synthesis.

3) Call the audio phase.

4) What methods of sound synthesis do you know?

5) List modern audio device interfaces.

Methodical instructions.

PC Sound System Structure

The PC sound system is structurally sound cards, or installed in the motherboard slot, or the other subsystem of the PC installed on the motherboard or the extension card.

The classic sound system, as shown in Figure 23, contains:

1. Record and sound playback module;

2. The synthesizer module;

3. Interface module;

4. Module Mixer;

5. Acoustic system.

Figure 23 - PC Sound System Structure

Synthesizer module

Effective sound system synthesizer allows you to generate almost any sounds, including the sound of real musical instruments. The principle of the synthesizer is illustrated in Figure 24.

Synthesis is the process of recreating the structure of the musical tone (notes). A sound signal of any musical instrument has several time phases. Figure 24, butthe phases of the sound signal arising when pressing ML of ML Vichy Piano are shown. For each musical instrument, the view of the signal will be peculiar, but three phases can be distinguished: attack, support and attenuation. The combination of these phases is called amplitude envelopethe form of which depends on the type of musical instrument. The duration of the attack for different musical instruments varies from units to several tens or even up to hundreds of milliseconds. In the phase, called support, the amplitude of the signal almost does not change, and the height of the musical tone is formed during support. The last phase, attenuation, corresponds to a plot of a fairly rapid decrease in the amplitude of the signal.

In modern synthesizers, the sound is created as follows. A digital device using one of the synthesis methods generates the so-called excitation signal with a given sound height (note), which must have spectral characteristics, as close as possible to the characteristics of the imitated musical instrument in the support phase, as shown in Figure 24, b.Next, the excitation signal is fed to the filter, simulating the amplitude-frequency response of the real musical instrument. An amplitude envelope of the same tool is applied to another filter input. Next, the totality of signals is processed in order to obtain special sound effects, for example, echo (reverb), choral performance. Next, a digital-based transformation and filters of the signal is performed using a low frequency filter (FNH).

The main characteristics of the synthesizer module:

Sound synthesis method;

Memory size;

The ability to hardware signal processing to create sound effects;

Polyphony - the maximum number of simultaneously reproducible sound elements.

Sound synthesis method,used in the PC sound system, it determines not only the sound quality, but also the composition of the system. In practice, synthesizers generating sound using the following methods are installed on the sound cards.

Figure 24 - Principle of operation of a modern synthesizer: A - Sound Signal Phases; B - Synthesizer Scheme

The method of synthesis based on frequency modulation ( Frequency Moduulation Synthesis -FM synthesis) implies use to generate a voice of a musical instrument at least two solid generators of complex shape. The carrier generator generates the main tone signal, the frequency-modulated signal of additional harmonics, overtones that determine the timbre of the sound tool. The envelope generator controls the amplitude of the resulting signal FM generator provides acceptable sound quality, has a low cost, but does not implement sound effects. In this regard, the audio cards using this method are not recommended in accordance with the RS99 standard.

Sound synthesis based on wave table Wave Table Synthesis -WT-synthesis) is made by using pre-digitized samples of the sound of real musical instruments and other sounds stored in a special ROM, made in the form of a memory chip or integrated in the WT generator's memory microcircuit. WT synthesizer provides high quality sound generation. This synthesis method is implemented in modern audio cards.

Memory sizeon the sound cards with the WT synthesizer, it may increase due to the installation of additional memory elements (ROM) for storing banks with tools.

Sound effectsformulate with a special processor effect, which can be either an independent element (chip), or integrate into the WT synthesizer. For the overwhelming majority of cards with WT-synthesis, the effects of reverb and chorus have become standard.

Synthesis of sound based on physical modeling provides for the use of mathematical models of sound formation of real musical instruments for generating digital form and for further conversion to a beep with a DAC. Sound cards using the physical modeling method have not yet been widespread, since there is a powerful PC for their operation.

Interface module

The interface module provides data exchange between the sound system and other external and internal devices.

ISA interfacein 1998, the PCI interface was displaced in the audio cards.

PCI interfaceprovides a wide bandwidth (for example, version 2.1 is more than 260 Mbps), which allows you to transmit audio data streams in parallel. Using the PCI bus allows you to improve the sound quality, providing signal-to-noise ratio over 90 dB. In addition, the PCI bus ensures the possibility of cooperative sound data processing, when the processing and data transmission tasks are distributed between the sound system and the CPU.

MIDI (Musical Instrument Digital Interface- The digital interface of musical instruments) is governed by a special standard containing specifications on the hardware interface: channel types, cables, ports, with which MIDI devices are connected one to another, as well as a description of the data exchange of information - information exchange protocol between MIDI devices. In particular, using MIDI commands can be controlled by lighting equipment, video equipment in the process of performing a musical group on the scene. Devices with MIDI interface are connected in series by forming a kind of MIDI network, which includes a controller - a control device, which can be used as a PC and a music key synthesizer, as well as driven devices (receivers), transmitting information to the controller by its request. The total length of the MIDI chain is not limited, but the maximum cable length between two MIDI devices should not exceed 15 meters.

The audio card includes an interface for connecting the CD-ROM drives.

7.5.4 Module Mixer

The sound card mixer module performs:

Switching (connection / disconnection) of sources and sound signals, as well as regulation of their level;

Mixing (mixing) multiple audio signals and adjust the level of the result.

The main characteristics of the mixer module include:

The number of mixed signals on the playback channel;

Adjustment of the signal level in each mixing signal;

Regulation of the level of the total signal;

Output power amplifier;

The presence of connectors to connect external and internal receivers / sources of sound signals.

Sources and sound signal receivers are connected to the mixer module through external or internal connectors. External sound system connectors are usually located on the rear panel of the system unit housing: JoyStick / Midi.- to connect a joystick or MIDI adapter; Mic In.- for connecting the microphone; Line In.- linear input to connect any sources of sound signals; Line Out.- linear output to connect any audio receivers; SPEAKERto connect headphones (headphones) or passive acoustic system.

Mixer software management is carried out either by Windows using a mixer program supplied with sound card software.

Standard Sound Blaster.support applications in the form of games for DOS, in which sound support is programmed with the orientation of the Sound Blaster Sound Card.

Standard Windows Sound System (WSS)microsoft includes a sound card and a software package focused mainly on a business application.

Examples of individual tasks

Model 1 - Sound Card SB PCI CMI 8738

Figure 25 - Appearance Sonic Card SB PCI CMI 8738

Description: Sound card with the ability to play audio in format 5.1

Type of equipment: multimedia sound card

Chip: C-Media 8738

Analog inputs: 2

Analog outputs: 3

Connectors: External: Line input, microphone input, output to the front speakers, access to the rear speakers, access to the center / subwoofer; Internal: Line input, CD input

The ability to connect 4 columns: yes

Support Dolby Digital 5.1: yes

EAX: EAX 1.0 and 2.0 support

Interface: PCI

The ability to connect 6 columns: yes

Model 2 - SB PCI TERRATEC AURON 5.1 PCI Sound Card