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#! /bin/bash
# Workaround for stupd 'powersave' 'feature' of Creative Speakers
#
# SJP 11 Dec 2021
#
# This is just a stub for now
# Which device is the audio output going to?
# st33v@cr4y:~$ grep RUNNING /proc/asound/card*/pcm*/sub*/status
# /proc/asound/card2/pcm0p/sub0/status:state: RUNNING
# That is fine, but the status remains as 'RUNNING' even after the speakers have turned themselves off...
# So I'm going down the track of periodically sending a 'sound' to a loopback device
# sudo modprobe snd-aloop
# Now aply -l shows a new 'card' called Loopback.
record one second of default stream:
$ rec -d -n trim 0 1 stat
rec sox in record mode
-d default input
-n direct output to /dev/null
trim 0 1 duration 1 second
stat
Output:
Input File : 'default' (pulseaudio)
Channels : 2
Sample Rate : 48000
Precision : 16-bit
Sample Encoding: 16-bit Signed Integer PCM
In:0.00% 00:00:01.02 [00:00:00.00] Out:48.0k [ | ] Clip:0
Samples read: 96000
Length (seconds): 1.000000
Scaled by: 2147483647.0
Maximum amplitude: 0.000000
Minimum amplitude: 0.000000
Midline amplitude: 0.000000
Mean norm: 0.000000
Mean amplitude: 0.000000
RMS amplitude: 0.000000
Maximum delta: 0.000000
Minimum delta: 0.000000
Mean delta: 0.000000
RMS delta: 0.000000
Rough frequency: -2147483648
Done.
So if Max amplitude = 0 then we have silence!
to generate a tone that is not audible:
play -n synth 1 sine 40 fade .2 0
play sox alias
-n dummy input file
synth synthesise a sound
sine sine wave [the default, so not strictly necessary]
40 Hz
fade fade in from zero volume to max volume over 200 msec.
'0' says fade out at end over same period.
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