Opus file starts with a noise impulse in LFE

[j7n]

There seems to be a bug with encoding 5.1 in Opus. The LFE channel sometimes starts with a quiet puff of noise at about -56 dB if the input contains inaudible background noise. Seems to happen in any recent version of Opus. There is no noise when encoding absolute silence. Can anyone confirm?

To reproduce: Make a silent file with 6 channels, add some dither to it, encode with opusenc.exe.

http://j7n.sytes.net/temp/opussample/

[Selur]

Can anyone confirm?
Not me.
With "opusenc opus-tools 0.2-34-g98f3ddc (using libopus 1.4-9-gc8549975)"
using:
ffmpeg -y -threads 8 -loglevel fatal -nostdin -i "C:\Users\Selur\Desktop\6chdither2s.wav" -ac 6 -ar 48000 -sample_fmt s32 -f sox - | sox --multi-threaded --temp "J:\tmp\2023-12-01@15_17_52_761000" --buffer 524288 -S -t sox - -t flac - | opusenc --bitrate 192 --comp 10 --framesize 20 --expect-loss 0 --max-delay 1000 --ignorelength - "G:\Output\iId_1_aid_0_2023-12-01@15_17_52_761000.opus"
and using:
opusenc --bitrate 192 --comp 10 --framesize 20 --expect-loss 0 --max-delay 1000 --ignorelength "C:\Users\Selur\Desktop\6chdither2s.wav" "G:\Output\direct.opus"
both seem fine. Can't here anything in MPC-HC nor see anything in audacity.

Cu Selur

[j7n]

I used the build from Rarewares and a few older ones with a simple command line:

opusenc --bitrate 448 6chdither2s.wav 6chdither2s.opus

The output of opusdec (https://i.imgur.com/eZvSDGD.png), Foobar 2.0 and MPC-HC is the same. It's quiet, but I first noticed it with quiet music. I suspect it might to do with filtering of the LFE because it can contain 4 kHz, but is lowpass filtered by the encoder.