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)

Typically external


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)


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, as a protocol very comparable to S/PDIF - the data format is actually largely the same.

The connection is more bothersome, though, for a few different reasons. For one, balanced AES3 (XLR connectors) isn't the same as unbalanced AES3 (BNC connectors) and neither is the same as S/PDIF (RCA connectors, assuming we're not talking optical). the voltage levels (assuming S/PDIF on copper, not fiber) are different for all three.

You can see AES3 is sort of an extended-definition variant of S/PDIF, with a differen

Defines interchange a little better:

Over XLR (IEC 60958 Type I)
Over RCA (IEC 60958 Type II)
Over TOSLINK (IEC 60958 Type III)
Over BNC - used in broadcasting as BNC/Coax is still common there.

The protocol is largely the same as S/PDIF, but extended somewhat

Two channels of PCM - at varied bitrates.

There is a spec of how to carry it over network with low latency


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


(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
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: