#262 Audio APC: A;Volume does not affect a voice queued at volume 0

[Rob Swindell]

A looping voice queued at volume 0 cannot be raised by a later A;Volume on its
channel. A voice queued at non-zero volume responds to A;Volume normally.

Repro

apc_loopvol_demo.bin (attached) is a raw audio-APC stream. In a shell inside a
SyncTERM session with audio enabled:

cat apc_loopvol_demo.bin

Two 1 s sine loops, identical except the A;Queue volume field:

• ch 3, 220 Hz — A;Queue loop vol 0, then A;Volume ch3=100
• ch 4, 440 Hz — A;Queue loop vol 100

apc_stop.bin flushes all channels.

Expected

Both tones (220+440 Hz chord).

Actual

Only 440 Hz. The volume-0 voice stays muted; the A;Volume has no effect.

Notes

Channels differ only in the A;Queue volume (0 vs 100). Stream built via
Synchronet's termgfx audio builders; libsndfile path.

[Stephen James Hurd]

The sample volume and the channel volume are different controls. A 0% volume is -60dB, and the channel volume defaults to -12dB for a total of -72dB. To get -60dB queue volume into the audible range, you would need to add positive gain to the channel, which you can't do with percentages. If you really need to do that, you could set the volume to 48dB, which would make -60dB into the normal -12dB... but any sample not played at 0% volume would blast it into to hard clipping.