Beware! Audio Editing Pitfall/Bug: Don't Waste Your Time With "High Quality Stretching" When Increasing the Speed/Tempo of a Song with the Free Software Audacity

Hello good people of Publish0x!

As some of you might know, I work as a fitness class instructor and have recently started uploading my fitness classes to my very new YouTube channel.

I have been composing workout playlists for a couple of years now and for that purpose, I learned some basic audio editing:

  • Cutting out parts of a song that I don't like / if the song is too long.
  • Repeating parts of a song if the song is too short (I am looking at all the 2-minutes-and-a-few-seconds-per-song-audio-producers...).
  • Speeding up the song or increasing its tempo if it's too slow or doesn't push hard enough.
  • Adjusting the bass, the treble and the pitch.

All of the above work really well with the free open source software Audacity -- available for Windows, Mac and Linux. (I can definitely recommend this software. By the way, this is not a sponsored recommendation. I don't earn a single Cent by recommending it.)

In addition to the above mentioned use cases, you can also use Audacity to slow down a song, but the results usually don't sound very convincing in my opinion.

As it turns out, Audacity has added an option for "high quality stretching" which should improve the results when you slow down a song. And herein lies

the pitfall -- or is it a bug?

-- that I discovered. I used the latest version of Audacity to increase the tempo of the song "Careless" by "NEFFEX" which I presented here on Publish0x in this post.

I decided to increase the song's tempo by about 8%. That might sound like a lot (and it is), but with previous versions of Audacity, I had increased the tempo of songs by more than 20% occasionally -- and the results sounded amazing. In the current version I found the option of "high quality stretching". "High quality" sounded good to me and I decided to use it. Even if it takes longer, the improved result would be worth it -- I thought.

Here is the comparison: More than 4 minutes for the "high quality" process


as opposed to about 8 seconds for the standard process.


To summarize: The "high quality" process took about 15 times as long as the standard process (more than 4 minutes instead of 8 seconds on my laptop with this specific song).

Let's listen

This is the version in which I used Audacity's "high quality stretching". The conversion took about 4 minutes and 15 seconds: 

And this is the version without "high quality stretching". It rather used the standard Audacity process. The conversion took about 8 seconds: 

Do you hear the difference? The first version sounds tinny. Not only did the "high quality audio stretching" take 15 times as long as the standard process, the result does not even sound as good as what we got with the fast standard process.  I have tested this with several other songs and came to the exact same result. The "high quality stretching" did not improve the sound quality when increasing a song's tempo. I can imagine that it improves the results if you decrease a song's tempo. If that is the case, then I really wonder why "high quality stretching" even exists as an option when you increase the tempo of a song -- it makes no sense to use it...

Conclusion: In case you want to use Audacity to increase a song's tempo or pitch, don't bother checking "high quality audio stretching". It's just a waste of time.

PS: Audacity's website states that the "high quality" algorithm is only suitable for "small to moderate tempo changes" without stating how much of a change is still considered "moderate". It seems that 8% is already more than a moderate tempo change... In my case, I will just stick with the fast algorithm.

PPS: In my next article I will explain how you can increase a song's tempo with Audacity. And I will discuss the difference between a song's tempo, it's speed and what pitch has to do with it. Stay tuned!
Update: Here is the promised article


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Workout Playlists
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