Adjusting quality of "Change tempo" & "Sliding..." effects

Hello everybody, I’m looking for a way to tell “Change tempo” or “Sliding Time Scale…” effects how to modify a piece of audio.

I did some tests slowing down the same file to a similar (very low) speed (0.30 the original speed), keeping the original pitch, and here’s what I got:

  • Audacity’s “Change Tempo” effect: there’s a lot of reverb-like side effect, because (I guess) the micro-parts of the original audio that are repeated to fill the longer time range are “too long”. A sort of stuttering…

  • VLC player (yes, the well-known one) setting playback speed at 0.30x: quite better than the previous one, but there’s still a (minor) stuttering/reverb effect. Apart from this, the sound (it’s a human speech, actually) is kept quite natural, as in the previous effect.

  • Audacity’s “Sliding Time Scale/Pitch Shift” effect: much smoother than the two above, very nice, but also rather “metallic” (a new side effect, not present in the other two effects - I said they were quite “natural”, indeed).

Ok, I know that: talking about tempo-change algorithms, it’s difficult to get perfect results, and we can’t have our cake and eat it too, but I was wondering if there’s one more effect to test or a way to adjust settings for the two mentioned above. I remember, since I had a look to it several years ago, that Adobe Audition (does it exist anymore?) included a main filter to change audio speed (keeping the pitch) where one could set, for example, the length of the micro-portions of audio that would have been used to “create” data where there were not (or a sort of that). Is this possible in Audacity, some way?

By the way, I was surprised when I listened to the performance of VLC player slow-downing “filter”: it’s much better than Audacity’s “Change Tempo”. Unfortunately, the “Sliding Time Scale/Pitch Shift” makes the human voice so metallic that I’d like to find an even better result.

I hope you have a greater knowledge than me to help me find a solution to this “problem”…

Thank you so much in advance.

P.S.: please forgive me if I did any language mistake, I’m not an English native speaker :slight_smile:

Oops! I forgot to say a couple of things: I’m using Audacity 2.0.3 on Windows 7 Ultimate.

“Sliding Time Stretch / Pitch Shift” is probably the best you’re going to get, but note that this effect does not like “noise”. The “cleaner” the original recording the better.
“Noise” (“shhhh”) when stretched turns into “zzzzzz” and may account for why your results sound metallic.

The Audacity “Change Tempo” is a quick and simple effect based on SoundTouch. The only user settings are those that you see. Quick and simple with reasonable (but not the best) quality.

For extreme time stretching you could try PaulStretch
This is designed for much more extreme time stretching than you are currently doing and will have quite a lot of “reverberation” to the sound, but it can stretch much further than any other time stretch tool than I’ve come across.

I think it’s not my case: the audio is a near perfect voice recording in the silence, it’s the ESLpod Podcast (here it is - - should you want to check the quality).

Anyway, thank you for your answer. I’ll test Paulstretch as soon as “Sliding Time…” effect will finish stretching a 17 minutes mp3 (25 minutes required) :slight_smile:

Thank you again :slight_smile: