Electronics project notes/Audio notes - Digital sound communication

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This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)


Typically external

S/PDIF

S/PDIF ("Sony/Philips Digital Interface") is purely the protocol.

Which is often carried over either

fiber, typically used with TOSLINK connectors
a single RCA connector on a coaxial cable, or


S/PDIF tends to carry either

raw PCM
surround (compressed, because of bandwidth limitations), often either:
DTS for 5.1/7.1 (which more specifically is the DTS Coherent Acoustics (DCA) codec
AC3 (Dolby Surround)



See also:

AES3

ADAT

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

ADAT has referred to two distinct things

Historically (and now rarely) to the Alesis Digital Audio Tape, a way of storing eight tracks digitally onto Super VHS


And much more typically to the ADAT Optical Interface, more commonly known as ADAT Lightpipe or often just ADAT, also from Alesis.

It looks the same as TOSLINK / S/PDIF, but speaks a different protocol, and somewhat faster.


It carries only 24 bit audio channels (though some devices will effectively work on the higest 16 for practical reasons).


Its speed lets it carry up to eight at 48kHz.

Or, with the common S/MUX extension, up to four at 96kHz, or two at 192kHz


See also:

Typically internal

I2S

(Note: no technical relation to I2C)

I2S (sometmimes IIS), Inter-IC Sound is meant to standardize PCM data between closeby chips.

It separates clock and data, means it can have somewhat lower jitter (and indirectly latency) than buses that don't.


It moves PCM data

16, 24, or 32-bit
stereo
8kHz to 192kHz (verify)

The sender should be somewhat comfigurable, because not all receiver necessarily implement all of that(verify)


As I2S doesn't spec a plug, or how to deal with longer cables (impedance and such), it is indeed mostly used within devices - exceptions mainly being audiophile setups that want to choose their DACs. (this takes care to do right, though, because impedance can cause synchronization issues, particularly at higher bitrates )


The lines are

  • bit clock (BCLK) (a.k.a. continuous serial clock (SCK))
  • left-right clock (LRCLK) (a.k.a. word clock, word select (WS), Frame sync (FS))
  • serial data
  • ground


Some also add a master clock (MCLK). This is not part of standard I2S, but can helps makes the DAC's timing a little more precise (DACs that don't need this may generate one internally).(verify)


BCLK pulses for each bit, so should be samplerate * bitdepth * channelamount, e.g. 1411200 Hz for CD audio

LRCLK selects left/right channel


See also:

On DACs