Sound Software

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Revision as of 13:44, 12 October 2011 by Dank (talk | contribs)

Sound on Linux is the absolute biggest bunch of bullshit ever, closely trailing sound on computers and sound itself.

Terminology

  • HDA: Intel High Definition Audio specification
  • ELD: EDID-Like Data. Structured capability data returned by graphics-oriented devices.
    • ELD can also mean Enhanced Low Delay (in for instance AAC-ELD)
  • PD/ELDV: Presence Detect/ELD-Valid bits aka "Unsolicited Responses".
    • PD indicates a change in presence or the ELDV bit
    • ELDV indicates new ELD information
  • EAX: Environmental audio eXtensions
  • S/PDIF: Sony/Phillips Digital Interconnect Format (IEC 60958 type II / IEC 958)
    • 10m max cable distance
    • TOSLINK F05 / EIAJ-Optical and coax RCA connections
    • Carries DTS and Dolby Digital compressed audio for >2 PCM (IEC 61937)
  • AES3: commercial-grade
    • 3-pin XLR (balanced) and BNC (unbalanced) connections
  • CDDA: CD Digital Audio, 2-channel 44.1k PCM
  • DAT: Digital Audio Tape, a 48k/44.1k/32k medium using 4mm magnetic tape

Hardware

I recommend the Xonar Essence ST PCI card for an in-machine solution.

USB DACs

  • Watch for true USB Audio Class 2.0 and solid asynchronous solutions
  • "The D-A Diaries" is an excellent article regarding the difficulties of producing accurate sound via USB output.
    • Essentially: USB has a clockless wire, thus there must be clocks on each side, which *will* drift
    • If the USB device doesn't have its own crystal, it might even time based off AC power

Kernel

  • Determine: are there still ALSA hardware drivers inferior to their OSS equivalents? Assuming no...
  • OSS emulation: kernel, library, or neither?
    • Kernel: snd_pcm_oss, snd_mixer_oss, snd_seq_oss provide /dev/dsp, /dev/seq, /dev/mixer
    • Library: aoss sets LD_PRELOAD to include libaoss.so
    • Neither: force fail on attempts to use OSS
      • Might be better if OSS-only code is old and crappy, as suggested by OSS-only nature, as it'll eliminate such code. Might also be better if OSS compatability introduces any kinds of issues. Might be worse if OSS code is better-written than ALSA code alternatives, and OSS compatability introduces no problems.

/proc/asound

  • /proc/asound/cards: Maps physical devices to ALSA card numbers
[eschatomatic](0) $ cat /proc/asound/cards
 0 [Intel          ]: HDA-Intel - HDA Intel
                      HDA Intel at 0xe8260000 irq 43
 1 [NVidia         ]: HDA-Intel - HDA NVidia
                      HDA NVidia at 0xe3080000 irq 17
[eschatomatic](0) $ 
  • /proc/asound/cardX: Device details indexed by ALSA card number, including codec and ELD dumps
    • NOTE: X being loaded is typically required for ELD detection!
  • /proc/asound/devices: Maps functional devices to ALSA card:dev number pairs and describes function
  • /proc/asound/modules: Maps kernel modules to ALSA card numbers
  • /proc/asound/pcm: Maps card:dev numbers to allocated PCM streams

ALSA configuration

  • What ought go in /etc/asoundrc? It's a complete enigma.
    • FIXME

HDMI

  • FIXME

Sound Servers

  • pulseaudio -- crashes mpd every time I try to use it (no longer true as of Fall 2008)
  • To drive ALSA through pulseaudio by default:
pcm.!default {
	type pulse
}

ctl.!default {
	type pulse
}
  • jack -- low-latency, professional software; it frightens me
  • esd -- deprecated, replaced by pulseaudio's esd-compat module

Hardware

  • PulseAudio can supposedly use a plugin together with HAL to drive dynamic devices

See Also