Electronics project notes/Audio notes - Digital sound communication

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The physical and human spects dealing with audio, video, and images

Vision and color perception: objectively describing color · the eyes and the brain · physics, numbers, and (non)linearity · color spaces · references, links, and unsorted stuff

Image: file formats · noise reduction · halftoning, dithering · illuminant correction · Image descriptors · Reverse image search · image feature and contour detection · OCR · Image - unsorted

Video: format notes · encoding notes · On display speed · Screen tearing and vsync


Audio physics and physiology: Basic sound physics · Human hearing, psychoacoustics · Descriptions used for sound and music

Noise stuff: Stray signals and noise · sound-related noise names · electronic non-coupled noise names · electronic coupled noise · ground loop · strategies to avoid coupled noise · Sampling, reproduction, and transmission distortions · (tape) noise reduction


Digital sound and processing: capture, storage, reproduction · on APIs (and latency) · programming and codecs · some glossary · Audio and signal processing - unsorted stuff

Music electronics: device voltage and impedance, audio and otherwise · amps and speakers · basic audio hacks · Simple ADCs and DACs · digital audio · multichannel and surround
On the stage side: microphones · studio and stage notes · Effects · sync


Electronic music: Some history, ways of making noises · Gaming synth

Modular synth (eurorack, mostly): sync · power supply · formats (physical, interconnects)


Unsorted: Visuals DIY · Signal analysis, modeling, processing (some audio, some more generic) · Music fingerprinting and identification

For more, see Category:Audio, video, images

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, or tell me)

This is mostly about hardware interconnects. For software media routing, see Local and network media routing notes

Typically external

S/PDIF

S/PDIF ("Sony/Philips Digital Interface") (a.k.a. IEC958) is purely the protocol, not a connector.

...but S/PDIF is often carried over either

fiber, typically used with TOSLINK connectors
a single RCA connector on (preferably) a coaxial cable


S/PDIF tends to carry either

  • raw PCM
  • surround (compressed, because of bandwidth limitations), often either:


See also:


Not to be confused with

  • AES/EBU (next section)

AES3

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, or tell me)


AES3, also marked AES/EBU, is a digital audio protocol very comparable to S/PDIF - the data format is actually largely the same, yet not qutie compatible.



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, 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 audio channels that are always 24 bit (devices that are 16-bit will effectively just use the 16 highest bits).

Its speed lets it carry

up to eight channels of those at 48kHz.

Or, with the common S/MUX extension

up to four channels at 96kHz
up to to two channels 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. Because it wasn't made for that, this takes more care to do right, 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