Signal Generator tool

This directory contains a developer tool that generates and outputs audio signals, via the Audio, AudioRenderer, GainControl and AudioOutputRoutingPolicy FIDL interfaces.

USAGE

signal_generator
  [--chans=<NUM_CHANS>]
  [--rate=<FRAME_RATE>]
  [--int16 | --int24]
  [--sine[=<FREQ>] | --square[=<FREQ>] | --saw[=<FREQ>] | --noise]
  [--amp=<AMPL>]
  [--dur=<DURATION_SEC>]
  [--frames=<PACKET_SIZE>]
  [--wav[=<FILEPATH>]]
  [--gain=<GAIN_DB>]
  [--ramp]
  [--endgain=<TARGET_GAIN_DB>]
  [--rampdur=<RAMP_DURATION_MSEC>]
  [--sgain=<SYSTEM_GAIN_DB>]
  [--smute[=0|=1]]
  [--last | --all]
  [--help | --?]

These optional parameters are interpreted as follows:

--chans=<NUM_CHANS>     Specify number of output channels (default 2)
--rate=<FRAME_RATE>     Set output frame rate in Hertz (default 48000)
--int16                 Emit signal as 16-bit integer (default float32)
--int24                 Emit signal as 24-in-32-bit int (default float32)

--sine[=<FREQ>]         Play sine of given frequency, in Hz (default 440.0)
--square[=<FREQ>]       Play square wave (default 440.0 Hz)
--saw[=<FREQ>]          Play rising sawtooth wave (default 440.0 Hz)
--noise                 Play pseudo-random 'white' noise
                        In the absence of any of the above, sine is played.

--amp=<AMPL>            Set signal amplitude (full-scale=1.0, default 0.5)

--dur=<DURATION>        Set playback length, in seconds (default 2.0)
--frames=<PACKET_SIZE>  Set packet size, in frames (default 480)

--wav[=<FILEPATH>]      Save to file (default /tmp/signal_generator.wav)
                        Gain/mute settings do not affect .file contents.
                        24-bit signals are saved in left-justified int32s.

--gain=<GAIN_DB>        Set AudioRenderer gain, in dB (default 0.0,
                        range [-160.0, +24.0]). If flag is absent, SetGain
                        is not called, so the stream plays at unity gain.

--ramp                  Smoothly ramp gain to -75.0 dB, over the signal's
                        duration. Values for end-of-ramp gain and ramp
                        duration are overridden by '--endgain' and
                        '--rampdur', respectively. If '--gain' is not
                        specified, ramping starts at unity gain.
--endgain=<GAIN_DB>     Ramp stream gain to the specified value (in dB),
                        instead of default -75.0 dB. (implies '--ramp')
--rampdur=<DURATION_MS> Ramp stream Gain over the specified duration (in
                        milliseconds), rather than the signal's entire
                        length. (implies '--ramp')

--sgain=<GAIN>          Set System Gain to [-160.0, 0.0] dB (default -12.0)
--smute[=<0|1>]         Set System Mute (1=mute, 0=unmute, default 1)
                        Changes to System Gain/Mute persist after playback.

--last                  Set 'Play to Most-Recently-Plugged' policy
--all                   Set 'Play to All' policy
                        Changes to audio policy persist after playback.

--help, --?             Show this message

IMPORTANT NOTE

Developers can use this tool to manipulate two important systemwide audio settings: system (“master”) gain/mute and audio output routing. Changes to these settings affect all audio output on the system and continue to have effect even after the signal_generator tool runs and exits. Only use the ‘--sgain’, ‘--smute’, ‘--last’ or ‘--all’ flags if you intend to change the system state in a persistent, “sticky” way.