1 PC Audio 2 Sound Card An expansion board that enables a computer to receive, manipulate and...
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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