[KVR Vishnu (VISHNU0906)]

Description

Fixes #3714.

AudioSpeedConverter changes speed by resampling the samples, so the pitch moves together with the speed. A 440 Hz tone at 2x comes out at about 880 Hz. The class docstring, the convert_async docstring and the audio converters doc page all said pitch was preserved, which is not what the code does. The issue also showed that a very large factor on a short input silently writes a file with zero samples.

The issue offered two routes: switch to a pitch-preserving time stretch, or correct the documented contract. I went with the smaller one here:

• the docstrings and the doc page (both the .py and the paired notebook) now say the pitch shifts with the speed, with the 440 Hz to 880 Hz example
• _resample_audio raises a clear ValueError when the factor would leave no samples, instead of writing empty audio

Behaviour for normal inputs is unchanged. If you would rather have a real pitch-preserving stretch, I am happy to look at that as a follow-up instead.

cc Roman Lutz (@romanlutz) (issue author). Happy to adjust anything.

Tests and Documentation

Added two tests in tests/unit/converter/test_audio_speed_converter.py:

• a 2x conversion of a 440 Hz sine shifts the peak to about 880 Hz, which pins the behaviour the docs now describe
• a 2-sample input at factor 100 raises ValueError instead of producing empty audio (fails on main, passes with the fix)

Locally, on a fresh clone of main:

• uv run pre-commit run --all-files: all hooks passed
• ty check pyrit tests/unit (the make ty target): all checks passed
• full unit suite (pytest -n 4 --dist=loadfile tests/unit): 32981 passed, 32 skipped

Docs updated in doc/code/converters/2_audio_converters.py and .ipynb (two comment lines each).

[Copilot]

🟡 Changes recommended

The two new async tests lack the _async naming suffix and parameter/return type annotations required by the style guide.

1 open issue

• Async tests are missing required naming and type annotations · New

What changed in this PR

Addresses #3714 by aligning AudioSpeedConverter documentation with its resampling behavior and preventing empty audio output, without changing normal conversions.

Changes:

• Clarifies that pitch shifts with playback speed.
• Raises ValueError when resampling would produce zero samples.
• Adds regression tests for pitch shifting and short-input rejection.

File	Description
tests/​unit/​converter/​test_audio_speed_converter.py	Adds pitch-shift and empty-output regression tests.
pyrit/​converter/​audio_speed_converter.py	Corrects docstrings and rejects zero-sample output.
doc/​code/​converters/​2_audio_converters.py	Updates documentation comments to describe pitch shifting.
doc/​code/​converters/​2_audio_converters.ipynb	Mirrors the documentation corrections in the notebook.

_{Review effort: Balanced}

[Adrian Gavrila (adrian-gavrila)]

Thanks for the fix!