Speed rendering issue/bug

Feedback and Discussion Forum Audacity 3.x Feedback and Reviews
1

Hi,
I am running Audacity 3.7.1 on Windows 11.
I am using Audacity to generate tones .wav file but not for audio purposes. So, I was trying to generate a 0.1Hz sinewave. Since the “Generate Tone” does not support below 1Hz, I used the “pitch/speed” tool to over sample the 1Hz tone 10x.
My procedure, on a 8kSPS, 16-bit PCM track:

  • Generate > Tone > Sine, 1Hz, 0.5s > Generate
  • Right click the track > Pitch and Speed > Set speed to 10% > Close

The visual render is as expected: half sinewave with a 5s duration. But, when I:

  • right click track > Render Pitch and Speed
    The tracks get all distorted. The same happens if instead of “Render Pitch and Speed” I simply export the visually good track as a .wav file. When I import the freshly exported track, I got the same distorted wave.

2025-04-07_13-55-09
2025-04-07_13-55-092080×3176 180 KB

2

To generate very low frequency tones, use the Nyquist Prompt effect.

This code will generate a sine tone at 0.1 Hz into the selected track region:

(hzosc 0.1)
3

Oh yeah, that works for wave generation. But why is the original rendering being altered?

4

When you first apply “Right click the track > Pitch and Speed > Set speed”, the waveform is visually stretched to show the correct length, but it is deceptive. It does NOT show the actual waveform of the stretched audio, it shows a stretched version of the waveform of the unstretched audio. Only when you render the speed change does it show the actual waveform of the stretched audio.