Public bug reported:
Create a frequency sweep using SoX, at 98% of full scale or above. Default is
100%. For example, use:
sox -n sin.wav synth 6 sin 10k:14k
Play that in Audacious. It ought to be a clean frequency sweep from 10
kHz to 14 kHz, but I hear other tones beating with it. The same thing
happens with PulseAudio and ALSA output. Other applications like aplay,
VLC and Chrome properly play the frequency sweep.
When using FileWrite WAV file output, Audacious creates a floating point WAV
file. That file does not contain distortion, but it creates samples exceeding
full scale, and plays with distortion in all players I've tried unless the
amplitude is reduced first. Converting it back to an integer WAV file:
sox -S sin.wav.wav -e signed-integer sin.wav-int.wav
results in a warning:
sox WARN sox: `sin.wav.wav' input clipped 32927 samples
The artifacts can be avoided if the frequency sweep uses 97% of full scale or
less, like:
sox -n sin-0.97.wav synth 6 sin 10k:14k vol 0.97
They're most obvious at high frequencies but can be seen in the whole
frequency range. The clipping creates odd harmonics, and then those
reflect back and forth due to aliasing. I am attaching a spectrogram of
a 10 Hz to 22 kHz sweep played via Audacious. There should just be one
bright line, without the harmonics and criss-crossing aliased images.
This seems to happen because Audacious converts samples to floating
point internally, slightly increasing the volume in the process. After
that, any conversion to integer without decreasing the volume will clip,
and conversion to integer is needed to play sound on most hardware.
The setting of the volume control is irrelevant. What matters is the
digital data being played. Typically, volume controls alter the
amplitude of the analog signal output from the DAC, and not the digital
signal itself.
ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: audacious 4.3.1-2.1build2
ProcVersionSignature: Ubuntu 6.8.0-60.63-generic 6.8.12
Uname: Linux 6.8.0-60-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.28.1-0ubuntu3.5
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: XFCE
Date: Fri May 23 14:53:59 2025
SourcePackage: audacious
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: audacious (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug noble third-party-packages
** Attachment added: "10 Hz to 22 kHz sweep played via Audacious"
https://bugs.launchpad.net/bugs/2111615/+attachment/5880017/+files/Audacious-sox-sweep-10-22k.png
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https://bugs.launchpad.net/bugs/2111615
Title:
Clipping and distortion above 97% full scale
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