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1st December 2023, 09:42 | #1 | Link |
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Join Date: Apr 2006
Posts: 137
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Opus file starts with a noise impulse in LFE
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/ |
1st December 2023, 15:28 | #2 | Link | |
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Join Date: Oct 2001
Location: Germany
Posts: 7,277
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Quote:
With "opusenc opus-tools 0.2-34-g98f3ddc (using libopus 1.4-9-gc8549975)" using: Code:
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" Code:
opusenc --bitrate 192 --comp 10 --framesize 20 --expect-loss 0 --max-delay 1000 --ignorelength "C:\Users\Selur\Desktop\6chdither2s.wav" "G:\Output\direct.opus" Cu Selur |
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1st December 2023, 16:56 | #3 | Link |
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Join Date: Apr 2006
Posts: 137
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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, 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. |
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