Audio peaking not accurately reflected in MuseScore Studio mixer

[MarekIwa]

Issue type

General playback bug

Description with steps to reproduce

When playing or exporting audio from MuseScore Studio, the actual signal appears to exceed 0 dBFS even though the mixer meters display levels below clipping.

As a result, users are unknowingly pushing audio beyond safe limits. The playback sounds somewhat clean inside MuseScore Studio, but once the same file is uploaded to MuseScore.com (and transcoded to MP3), peaks are clipped, resulting in audible distortion.

Steps to reproduce the issue:

1. Open any score in MuseScore Studio.
2. Insert a audio monitoring plugin (e.g., iZotope Insight, Ozone 11, or Waves metering tools) on the master channel.
3. Play the score in MuseScore Studio and compare the external meter readings with the monitoring

You’ll observe the external meters showing levels exceeding 0 dBFS, while MuseScore Studio’s meters remain below the peak threshold.

Export the score to WAV and analyze the waveform — peaks will be above 0 dBFS.
Upload the same score to MuseScore.com and play it back — the transcoded MP3 will exhibit audible distortion..

Supporting files, videos and screenshots

https://drive.google.com/file/d/1m_AUWdXH_uQi1aGVWioqs7-_ToZWpmWK/view?usp=sharing

In which versions of MuseScore Studio is this issue present?

4.6.3

Regression

No.

Operating system

Windows 11

Additional context

No response

Checklist

• This report follows the guidelines for reporting bugs and issues
• I have verified that this issue has not been logged before, by searching the issue tracker for similar issues
• I have attached all requested files and information to this report
• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible

[jessjwilliamson]

Yes, can confirm - this goes back to the first release (4.0) and is also the same on MacOS.
Here's a simple screen shot to show the issue that I'm testing on MuseScore 4.0.2:
An example where the master meter on mixer shows below -12dB but the actual output shows -5dB

[MarekIwa]

@jessjwilliamson, note that the 'FM8' stem also has incorrect values. This implies the problem is mixer-wide.