[opus] Opus 1.5.2 low hum in input file results overblown output at decoding

Tue Jan 28 18:53:01 UTC 2025

Thanks for looking into this. I've played with the options I'm setting on the decoder and narrowed the issue down to DTX. If DTX is enabled, I get the reported behavior, but it does not happen with DTX disabled.

I've posted a revised example:
https://github.com/xiph/opus/issues/382

In this new version, I've removed the Microsoft-specific code and it runs/reproduces on Linux now as well. Also, to simplify things further, I replaced the mu-law input file with a linear16 sample file and removed the extra code to do the conversion from mu-law to linear in the sample app.

I don't believe that the opustools utilities support controlling DTX option, so I don't think this can be reproduced using those tools. But if you have a built opus and a recent C++ compiler, it should be dead simple to compile and run this sample application. I put an example command line for compiling under Linux in the README.

My application is mostly network transmitted audio (RTP) containing speech, so disabling DTX is very undesirable.

Kevin O'Connor

-----Original Message-----
From: opus <opus-bounces at xiph.org> On Behalf Of Petr Parízek
Sent: Friday, January 24, 2025 12:03 PM
To: opus at xiph.org
Subject: Re: [opus] Opus 1.5.2 low hum in input file results overblown output at decoding

 EXTERNAL EMAIL - Please use caution with links and attachments 

There was a post in the Opus subthread on HA where there was a link to the file called Opus-tools-0.2-34-g98f3ddc_(using_libopus_1.5.2-21-gff6dea5)_Win_GCC142.7z.
That's the one I'm currently using.
First, I used GoldWave to convert your input file from µ-law to PCM and saved it as a ".wav" file.
Next, I encoded it with Opusenc, I decoded its result with Opusdec with the target sample rate being set to 48 kHz, and I got no excessive amplification.
Not sure what's taking place on your side.

Petr

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