Lecture Nine Sound Cards

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Lecture NineSound Cards
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Anatomy of a Sound Card
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Digital Audio Replay Recording

• Matched pair of D-to-A and A-to-D converters
• Programmable sample rate generator
• rates usually fractions of 44.1kHz
• latest cards are using fractions of 48kHz (DAT)
• best cards are using 96kHz (professional systems)
• Full-duplex operation only on better cards
• needs 2 DMA channels gt complex installation

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MIDI Synthesiser

• FM synthesis
• mathematical descriptions of the characteristics
  of musical instruments
• get a facsimile of the instrument playing the
  note
• Wave-table synthesis
• much more realistic (c.f. a piano sound on each)
• uses samples of actual sounds made by real
  musical instruments

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Wave-tables

• One or more samples for each instrument.
• Sound cards vary in their polyphony, i.e. the
  maximum number of notes which can be played at
  once, e.g. 8 or 16.
• Wave-table can be held in ROM or RAM (the latter
  allowing download from the host).
• DSP chip may offer other effects, e.g. reverb.

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MOD files

• A de-facto standard in computer games industry
• File contains the sample data (c.f. MIDI) song
• Song is specified as series of steps (16/bar)
• pitch of the note
• which sample is to be used
• modifications to the sample, e.g. vibrato
• Ability to loop sections, e.g. for rhythm