Issue when changing tempo of a selection twice

Audacity Help Forum Windows
1

Hi, I’m using Audacity 2.0.6 and when you select a fragment of an audio, and change tempo twice (select a section, then apply change tempo, and then again apply change tempo), the resulting fragment has a corrupt end:

In this example, I selected a fragment from 1:05:40 to 1:20:90. The issue appears at the end of the selection.

That GAP in the minute 1:20:90 shouldn’t exist, and appears when you change tempo twice in the same selected fragment. Fix it, please!

Thanks! :stuck_out_tongue:

2

Maybe its problem with ur drivers? r they actually?

3

It’s nothing to do with drivers.

Yes, that’s normal - not ideal, but normal.

The problem is that “time stretching” is rather difficult to do. Audacity uses two methods of time stretching. One method is “synchronized overlap-add method (SOLA)”, which is used in “Change Tempo” and “Change Pitch”. The other is “Subband Sinusoidal Modeling Synthesis (SBSMS)”, used in the “Sliding Time Scale / Pitch Shift” effect.

SBSMS usually sounds better than SOLA, and it does not have the problem of mangling the ends, but it is much slower than SOLA.
If the exact duration and “not mangled ends” are important, use the “Sliding Time Scale / Pitch Shift” effect.
If the ends are not so important but you want something quick and easy, use “Change Tempo”.

Note that for some types of material, Change Tempo / Change Pitch may sound better than “Sliding Time Scale / Pitch Shift”, but usually “Sliding Time Scale / Pitch Shift” sounds better.

The “Sliding Time Scale / Pitch Shift” effect is described here in the manual: Audacity Manual

4

And note that your signal is oversaturated - the meters are showing reda t their right end and the waveforms are touching the top and bottom of their panel.

A good level to aim for is -6 dB on the meters which corresponds to 0.5 on the linear scale of the waveform.

You can do yourself a big favour and enlarge the meters by clicking and dragging on the right end of the meter toolbar, makes setting the levels much easier (and things should improve further with the next release of Audacity as we are experimenting with improved meters).

WC

5

Thank you so much, Steve, for the explanation. The thing is that I think this didn’t happen in Audacity 2.0.5. I’d swear that in all the time I’ve been using Audacity, I’ve changed the tempo twice and more times in the same section, and never faced this issue.

About the saturated wave, I know, but it sounds OK, it came like that the song. Some songs I import that have very good quality also have this over saturated wave, but they still sound amazing. I don’t understand what “enlarging the meters makes setting the levels much easier” means. What is being improved?

Thanks! :wink:

6

It did :wink:
The interface has changed a little, but the effect itself has been the same for many years.
If the selected audio starts and ends at silences, then you can often get away with it (the mess at the end is not noticeable).

7

With the default size meters that you have in your screenshot they are so narrow that it is hard to see when you are at the optimal -6 dB level. Making them wider increases the accuracy that can be observed (I stretch mine across the whole width of the window).
See this page in the Manual: Audacity Manual

Assuming that things stay as they are now in the alpha version:

  1. The coloring of the meters will change to be green when a good signal level, fading to yellow and then red for saturated signals.
  2. The two meters will be two separate toolbars which means that each can be sized separately. I still have mine stretched across the whole window but now I have the recording meter taking up 3/4 of the width (for me that’s by far the more important meter).
  3. The dropdown menu options are improved.
  4. The older (current) form of the meters is likely to remain as an option for folks who don’t want or like the new ones.

You can see for yourself if you download the latest alpha nightly: gaclrecords.org.uk

WC