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PC AudioPC Audio

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Sound CardSound Card

An expansion board that enables a computer to receive, manipulate and output sounds

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Sound Card ComponentsSound Card Components

A typical sound card may include:A/D and D/A convertersHardware and software to permit recording and

playback of 16-bit audio at multiple sampling ratesSoftware controlled audio mixerDigital I/OCD Analogue Audio inputOn-board power amplifiersAnalogue line in/out jacks, microphone input,

joystick/MIDI connector FM synthesiser Wavetable synthesiser

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Sound CardSound Card

PCI connector

A/D and D/A converters

DSP

SPDIFF Digital output CD SPDIFF digital input

Digital I/O (audio extension connector)

CD Analogue Audio input

Wave table and FM

Synthesizer

SPDIFF Digital output

Line in jack

Microphone jack

Line out jack

Joystick/MIDI connector

Power amp

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PC Busses and InterfacesPC Busses and Interfaces

Sound cards are usually connected to the processor via either:Industry Standard Architecture (ISA)bus

• 11 Mbyte/sec

Peripheral Component Interconnect (PCI) bus• 132 Mbyte/sec

• Efficiently integrates the computer’s processor and memory with peripherals

• Has replaced the ISA bus on most modern PCs

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PC Busses and InterfacesPC Busses and Interfaces

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PC Busses and InterfacesPC Busses and Interfaces

CD-ROM is connected to the processor via IDE or EIDE (Enhanced Integrated Drive Electronics) bus

Burst speeds up to 16Mbytes/second

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Digital I/ODigital I/O

Some cards provide a direct digital output using an optical or coaxial S/PDIFF (Sony/Philips Digital Interchange Format) connection

For connecting to other digital devices:Input from CD/DVD-ROM driveIn/Out to DAT and MiniDisc recordersOutput to digital speakers

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CD Analogue Audio InputCD Analogue Audio Input

Connects from the analogue audio output on the CD or DVD-ROM drive using a CD audio cable

Provides similar analogue line audio signal as that output from the headphone socket

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Digital Audio ExtractionDigital Audio Extraction

DAE also known as “ripping” is the process of moving a Red Book track on a CD, usually music, to a hard drive or other storage medium

In theory DAE enables you to extract digital audio via your EIDE interface from a CD at the speed of your CD-ROM drive

In reality this can be problematic

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Digital Audio ExtractionDigital Audio Extraction

Redbook audio format supposes that data will be read in a continuous spiralThus there is no addressing provisionData written onto a CD-ROM must be read

continuously with no stopsCD audio data is stored as frames

There is no unique identifier for each frameApproximate positioning is provided by the

frame subcode over 98 frames, 1/75th second

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Digital Audio ExtractionDigital Audio Extraction

In DAE large data files are moved from the CD-ROM drive to the hard diskThis can not happen continuouslyIntermediate buffers are filled and emptied

Thus, CD-ROM drive will read sectors in short burstsAs positioning is not exact, small clicks and

pops may appear in the musicSpecial software/ hardware is required to

overcome these synchronisation errors

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Line In/OutLine In/Out

Standard type of audio signal to minimise noise and distortion when:processing soundtransferring it from one component to anotherreproducing recorded sound

1v peak to peakNot really enough to drive non amplified

speakersBut larger than the mic input

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SynthesisSynthesis

There are two main techniques for creating sounds in music synthesisersFrequency Modulation (FM) synthesis - uses

one periodic signal (the modulator) to modulate the frequency of another signal (the carrier)

Wavetable synthesis – uses short samples from the original instrument

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FM SynthesisFM Synthesis

Each FM voice requires a minimum of two signal generators

Sophisticated FM systems may use 4 or 6 operators per voice

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Wavetable synthesisWavetable synthesis

Stores high quality sound samples digitally, and then replays these sounds on demand

For many instrument sounds, the sound can be modelled as consisting of two major sections: attack sustain

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Windows Multimedia APIWindows Multimedia API

Allows access to the sound card functionalityBut is limited to the access functions that

windows providesNo direct means of mixing

DirectX APIProvides real-time low level access to sound

card• Functions for mixing, controlling volume, balance

etc.

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Universal Serial BusUniversal Serial Bus

USB provides fast, user friendly I/O device connection12 Mbps (slow but faster than the serial ports)Sufficient for applications using:

• S/PDIF

• MPEG-1 and some MPEG-2

Future versions 120 – 240Mbps

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Digital SpeakersDigital Speakers

Connect to USBContain:

D/A converterAmplifier Less susceptible to interference

Max run of a USB cable is 5 M

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FinFin

Fin