Warbling bass notes

Hi
Using Audacity 1.3.9. I transposed a piece of music from A down to G using the ‘Change Pitch’ effect. Seemed to work OK but I’ve noticed on the transposed version the lower notes have become ‘Warbly’ - bit like Wow on a tape machine. Is there anything I can do to reduce / stop this effect please?

I am downloading free backing tracks, tidying them up in Audacity and converting them to MP3 for my MP3 player. It obviously helps if the volume levels of these tracks are more or less consistent to save reaching for the volume control whilst playing some inspired lead line. I am trying to understand exactly what affects what when setting levels. When converting the tracks to MP3, does the position of the Output slider affect the MP3 level or does the fact that the tracks have been normalised to -3db ensure that the recorded MP3 file is also normalised to -3db. I appreciate that the audio output signal level will depend on the MP3 to audio conversion device be it the computer sound card or the MP3 player.

I take it that 0db on the meter is the absolute max before clipping takes place. If so then -2db or -3db seems a sensible recording level. This is easily achieved using the ‘Normalise’ effect set to -3.0db. Is this the best recording level to use? Any reason for changing to some other level?

Sorry if I’ve rambled a bit.

Many thanks
Jim

Changing the pitch of music without changing the tempo is a difficult effect to achieve (it requires chopping the sound up into little pieces, re-spacing them, then sticking them all back together again). Changing the “Speed” (pitch and tempo both change) is much more simple and Audacity can do this almost perfectly. If your project could cope with being a little bit slower, then you could use the “Change Speed” effect.

I’m guessing that you don’t want to do that - so moving swiftly onto plan “B”.

Audacity 1.3.12 has an effect called “Sliding Time Scale/Pitch Shift”. This effect can perform higher quality pitch changing than the normal “Change Pitch” effect. There are however 2 drawbacks -

  1. It is very slow (processing takes ages).
  2. The version in Audacity 1.3.12 is rather buggy and may crash.

The developer of this effect has been working on both of these problems and made considerable improvements to both speed and stability (though it’s still slower than the normal “Change Speed” effect). The latest version of this effect is available in the “Nightly” version of Audacity: Missing features - Audacity Support
The Windows versions are packaged as ZIP files - to use them, just extract the contents of the ZIP file somewhere on your hard drive, then create a link (shortcut) to the audacity.exe file.

What about resampling at a higher rate before applying the pitch change, then resampling back to the original rate afterwards.

Resampling to a higher rate can make a marginal improvement, but it is not much better.
The “Sliding Time Scale/Pitch Shift” is not quite right yet, but the sound quality is a lot better.

The attached file is a couple of low piano notes shifted down by 2 semi-tones.

The first part is using the standard Change Pitch effect at 44100 Hz
The second part is using the standard Change Pitch effect at 192000 Hz
The third part is using the “Sliding Time Scale/Pitch Shift” at 44100 Hz (Audacity ® 1.3.13-alpha-Jun 28 2010)

Forgot to mention - The errors in the current Audacity Nightly version of “Sliding Time Scale/Pitch Shift”:
The pitch controls are also the wrong way round - use negative values to go higher in pitch.
The sample rate is 44100Hz for the change in pitch to be as predicted by the settings.
Apparently both of these errors have now been fixed but the fixes have not yet been commited into the Audacity code https://forum.audacityteam.org/t/sliding-pitch-and-time-crash/14284/1

Comparing the spectra of the 44100 Hz and 192000 Hz manipulated piano recordings the difference is very slight, (the black bits) …


The new 1.3.13* “Sliding Time Scale/Pitch Shift” sounds very much better.

[* developers are not superstitious then :slight_smile: ]

Hi
Just got back to the forum. Thanks for the info. I’ll give that a try. The warbly sound of my backing track is so offputting.

Regards
Jim

Hi again
Just tried transposing from A down to G. I had to put +2.0 in the pitch shift boxes. Tested it by generating a pure tone of 220 Hz, pitch shifting and checking the result on my guitar. Happy with that so I transposed the backing track. Also ticked Dynamic Transient Sharpening. This certainly slowed it down. However, for the results obtained that is a small price to pay. Thanks to everyone for producing this useful piece of software.
Regards
Jim

Apparently that will be corrected in the next Audacity release (it should of course be -2.0 to transpose from A down to G).