sps-alsa-explore

Purpose

This command-line application scans for alsa devices that can be used by Shairport Sync.

It does this by attempting to open every alsa device it can find for two-channel interleaved operation at frame rates that are multiples of 44100 with linear integer sample formats of 32, 24, 16 and 8 bits.

If successful, it lists any decibel-mapped mixers found on the device for possible use by Shairport Sync.

It also suggests the frame rate and format that would be chosen by Shairport Sync in automatic mode.

Docker Image

sps-alsa-explore is available on the Docker Hub at mikebrady/sps-alsa-explore. Alternatively, you can build it using the following guide.

Building

In the commands below, note the convention that a # prompt means you are in superuser mode and a $ prompt means you are in a regular unprivileged user mode. You can use sudo ("SUperuser DO") to temporarily promote yourself from user to superuser, if permitted. For example, if you want to execute apt-get update in superuser mode and you are in user mode, enter sudo apt-get update.

Prerequisites

# apt update
# apt install --no-install-recommends build-essential git autoconf automake libtool libasound2-dev

Download and Build

$ git clone https://github.com/mikebrady/sps-alsa-explore.git
$ cd sps-alsa-explore
$ autoreconf -fi
$ ./configure
$ make

Use and Sample Output

Note that the user running this tool must be a member of the audio group, or must be the root user. To run the tool from the directory in which it was compiled:

$ ./sps-alsa-explore
> Device:              "hw:Intel"
  Short Name:          "hw:0"
  This device seems suitable for use with Shairport Sync.
  Possible mixers:     "Master"              Range:  74.00 dB
                       "PCM"                 Range:  51.00 dB
  The following rate and format will be chosen by Shairport Sync in "auto" mode:
     Rate              Format
     44100             S16_LE

> Device:              "hw:sndrpihifiberry"
  Short Name:          "hw:1"
  This device is already in use and can not be checked.
  To check it, take it out of use and try again.

> Device:              "hw:vc4hdmi"
  Short Name:          "hw:2"
  This device can not be accessed and so can not be checked.
  (Does it need to be configured or connected?)

Unfortunately, there doesn't seem to be a consistent or logical way to tell which mixer is the best one to use.