bit perfect audio on linux

Pushing audio bits straight to dedicated audio hardware. For example, sending raw 16bit PCM at 44kHz straight to a DAC. This seems like a reasonable goal if you've got the right hardware, Right?

It still requires some attention but pipewire has improved things.

You will need some hardware, a USB DAC is ideal. It should support the most sample types and frequencies. Lower on the list are HDMI, Coaxial, and Optical. Optical sounds the best as lasers can't get interference from ground loops, can be used by sharks, etc. but it isn't. Toslink doesn't have enough bandwidth for more than two uncompressed channels of audio. Yes, I was disappointed too.

ALSA

This is the backend where the bits leave the computer. This is useful to see what we are actually piping out to the world and you have a long way to go if you don't see anything here.

capabilities

aplay -l or -L will tell you about your devices. HDMI audio is a thing so you will probably have more devices than you expected. For a DAC, you will want to find the usbstream:CARD=DAC. With the card number X we can see the capabilities: cat /proc/asound/cardX/stream0

  Interface 1
    Altset 1
    Format: S32_LE
    Channels: 2
    Endpoint: 0x01 (1 OUT) (ASYNC)
    Rates: 44100, 48000, 88200, 96000, 176400, 192000, 352800, 384000, 705600, 768000
    Data packet interval: 125 us
    Bits: 32
    Channel map: FL FR
    Sync Endpoint: 0x81 (1 IN)
    Sync EP Interface: 1
    Sync EP Altset: 1
    Implicit Feedback Mode: No

If you're lucky, you might see Format: SPECIAL DSD_U32_BE for more complicated setups than I will cover.

older optical info

With aplay -L you'll want to see that you have a iec958 (optical out) device.

iec958:CARD=PCH,DEV=0
    HDA Intel PCH, ALC892 Digital
    IEC958 (S/PDIF) Digital Audio Output

pipewire

config pipewire wiki

Config files should be copied from /usr/share/pipewire/ to the user path ~/.config/pipewire/.

In the pipewire.conf, you can change the default rate and allowed-rates to match your hardware.

    ## Properties for the DSP configuration.
    default.clock.rate          = 96000
    default.clock.allowed-rates = [ 44100 48000 88200 96000 176400 192000 352800 384000 ]

restart this all after changing: systemctl --user restart wireplumber pipewire pipewire-pulse

verify with: pw-metadata -n settings | grep clock.allowed.rates

watch the outputs: pw-top

other useful tools: pw-cli ls Device pw-dump pw-cat pw-play

resampling is another story, maybe for another day.

pipewire @ arch

audophile @ endeavouros

wireplumber

wireplumber @ arch

verification

Check to see what format and bitrate is actually being used by the device:

~ cat /proc/asound/card0/pcm1p/sub0/hw_params

access: MMAP_INTERLEAVED
format: S16_LE
subformat: STD
channels: 2
rate: 48000 (48000/1)
period_size: 44100
buffer_size: 88200

software players

Pipewire comes with a simple pw-play command, which should do the right thing by default.

configure DeaDBeeF

Setup pipewire output and it should do the right thing. Formerly I had this set to pipe straight to the ALSA device. With Optical output, this would cause glitches when moving from a high bitrate to a lower one (96k -> 44k).

configure Audacious

Does not do the right thing yet.

DSD

native DSD playback with pipewire

iecset - IEC958 controls

This seems like an interesting tool to dump optical output information, even if it doesn't appear to do much in consumer mode.

iecset -Dhw:1 head-fi bit-perfect-audio-from-linux

quake soundtrack

The audio bits lie! (sorta) Quake's audio soundtrack was a haunting ambient score by NIN which as pressed as extra tracks after the data.

It was recorded to the cd with pre-emphasis applied to the tracks. This means that the higher frequencies would be boosted prior to writing the tracks, resulting in a better signal to noise ratio. If you use a dedicated CD device or direct line, the emphasis bit will be detected, boost removed, and you hear what you expect. Unfortunately, if you read the tracks as data for copying to flac, the boost will persist and you'll have a heavy high frequency version of the soundtrack. This is well handled with SoX but it took me an embarrassingly long amount of time actually learn emphasis existed in spite of decades of listening to this cd.

quake soundtrack solutions - source of the enlightenment.

In 2020 it was remastered on vinyl. Apart from missing a nice booklet, the pre-emphasis was also absent for final verification.

*NOTE
WE DESIGNED THIS REISSUE TO INCLUDE A BOOKLET CONTAINING ESSAYS FROM ID SOFTWARE’S JOHN CARMACK AND AMERICAN MCGEE. A CERTAIN UNNAMED VIDEO GAME PUBLISHER MADE IT IMPOSSIBLE TO INCLUDE THIS IN THE PACKAGE, SO PLEASE HONOR THEIR WISHES BY NOT CLICKING HERE TO EVEN SEE THE ESSAYS OR HERE TO PRINT THE BOOKLET OUT FOR YOURSELF

quake - nin wiki