Fine 'Change Speed' Effect?

[yakev724]

Quick question:

I've got an audio track (4 min) that I'd like to compress by 220ms. The 'Change Speed' effect can do this if it allowed for finer adjustment than 10^-3. If I try to enter anything more specific, it rounds down to 0.999. Any alternatives? Other software? Tweak in code?

Thanks in advance.

[steve]

A speed change of 0.092% will compress a 4 minute track by 221 ms. If that's not accurate enough, just compress part of the track by a further 0.001%, but it begs the question why do you need to compress a track to greater accurately than 1 millisecond over 4 minutes?

[yakev724]

I misunderstood the notation of the program.

Instead of 0.999 of the track, it actually adjusts by 0.999 of a %, so allows for 10^-5 instead of 10^-3 adjustment as I originally thought.

Got exactly what I wanted, thanks for replying!

[billw58]

There is a feature request on the wiki "Change Speed to have length of selection control as well as Change Tempo (4 votes)". You can find this on
http://wiki.audacityteam.org/wiki/Featu ... to_Effects

There is a note in that section:

You can calculate the required exact percentage change thus:
( (BPM to) - (BPM from) ) / (BPM from) * 100 = % change e.g. 138.8 BPM to 145 BPM is
(145-138.8) = 6.2 / 138.8 = 0.044669 * 100 = 4.4669

Rather than go through that calculation I'd like to have two "spinboxes" (as in the Selection Toolbar and the Generate effects) to show the original length and target length in whatever resolution you'd like. I'm going to add my vote for that feature. Would you like me to add your vote as well?

-- Bill

[steve]

Could you add my vote while you're there Bill. I'm forever forgetting which has to be divided by what and it should be really easy for the effect to calculate it.

[billw58]

I'm forever forgetting which has to be divided by what

Me too! It's one thing to figure "I want it shorter so it has to be faster" but do I divide by the original length or the new length? Turns out you divide by the new length.

I've added notes in the manual on the Change Speed and Change Tempo pages about those calculations. And I actually tried the change speed calculation to make sure I had it right!

-- Bill

[steve]

How about something like this.
The attachment is a Nyquist Plug-in that can be installed by copying into the Audacity Plug-ins folder and restarting Audacity. It will appear "below the line" in the Effect menu.

Unfortunately the sample rate conversion quality is not quite as good in Nyquist Plug-ins as the built-in effects in Audacity, but it's not bad and it's fairly quick.
(Note, there is only basic error checking against invalid user input in this version so some invalid input may cause unexpected results).

[Gale Andrews]

Could you add my vote while you're there Bill. I'm forever forgetting which has to be divided by what and it should be really easy for the effect to calculate it.

Done (and I added three other stored votes I had from others too):
http://wiki.audacityteam.org/wiki/Featu ... to_Effects

Thanks for the notes, Bill, in the Manual about how to calculate speed change. I'd been wanting to add something about this to Wiki too, so I'll add a "Change Speed" page there presently with this and other tips.



Gale

[steve]

There's a proposal on the Audacity wiki for enhancing the Change Speed effect by adding the ability to select the final duration: http://wiki.audacityteam.org/wiki/Propo ... hancements