Change tempo without changing pitch

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rossmcm
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Change tempo without changing pitch

Post by rossmcm » Mon Mar 30, 2015 6:22 pm

I use this effect a lot for producing half-speed versions of recordings or learning purposes. It's pretty easy to use, but the quality is lacking, I suppose due to the trip into the frequency domain and back again.

It occurs to me that the case of slowing a recording down by a factor of exactly 2 could be a special case where better results can be achieved using the knowledge that the ratio between the original and output waveforms is an integer.

Is this worth pursuing? Does anyone know how the existing effect is implemented?

Thanks,
R

steve
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Re: Change tempo without changing pitch

Post by steve » Mon Mar 30, 2015 8:05 pm

The "Sliding Time Scale / Pitch Shift" effect takes a lot longer to process, but the sound quality is usually much better.
See: http://manual.audacityteam.org/o/man/sl ... shift.html
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rossmcm
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Re: Change tempo without changing pitch

Post by rossmcm » Mon Mar 30, 2015 8:19 pm

Brilliant! I just tried it and the results are much, much better. Thanks.

In fact, as a test I slowed down a track to half-speed, then used the function again to speed it up to the original tempo, and the results were pretty much indistinguishable from the original.

As an aside, I do find the way that the new tempo is specified a bit confusing, and wonder if it wouldn't be useful to have a field labelled as "Ratio of new tempo to original (0.5 to 2.0)"

R

steve
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Re: Change tempo without changing pitch

Post by steve » Mon Mar 30, 2015 8:35 pm

rossmcm wrote:As an aside, I do find the way that the new tempo is specified a bit confusing, and wonder if it wouldn't be useful to have a field labelled as "Ratio of new tempo to original (0.5 to 2.0)"
That would be possible, but I think there is a limit to the number of ways of specifying the same thing. Already we have: "Percent" as a number. "Percent" as a slider, "beats per minute" and "From / To length", so that's 4 sets of controls that all do the same thing. One of the advantages of the "percent" amount is that the numbers correspond across all of the time stretch type effects (Change Speed / Change Tempo / Change Pitch / Sliding Time Scale Pitch Shift).

In the new Audacity 2.1.0 (new out today), the "Change Speed" effect has been updated so that you can enter the change as a "multiplier" (half speed = 0.5, double speed = 2.0), If you have difficulty working out the percent change for the Change Tempo effect, you can "cheat" by opening the Change Speed effect and use that to work out the percentage for you. (see: http://manual.audacityteam.org/o/man/change_speed.html)
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rossmcm
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Re: Change tempo without changing pitch

Post by rossmcm » Mon Mar 30, 2015 9:33 pm

OK, that's pretty much what I am talking about.

Either a pair of fields: Beats per minute From: _______ To: _______ like in the Change Tempo dialog, or (in the Sliding time scale/Time shift dialog) you could have Speed Multiplier fields next to the Percentage Shift fields and have them linked so changing one also changes the other.

kozikowski
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Re: Change tempo without changing pitch

Post by kozikowski » Mon Mar 30, 2015 10:30 pm

It could be argued that the two tools are backwards. "We can produce trash really quickly and conveniently as default ..."

Nobody I know got up in the morning saying, "I think I'll produce some really sub-quality work today."

I'd much rather tell people there is a much faster way to do this job, but the quality isn't nearly as good.

Koz

steve
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Re: Change tempo without changing pitch

Post by steve » Mon Mar 30, 2015 10:36 pm

kozikowski wrote:It could be argued that the two tools are backwards.
Yes it could be, but you're aware of the historical background. The Change Speed / Tempo / Pitch suite was well established long before the first version of STS/PS, and the latter still has some issues, such as no Preview.

Perhaps a better argument would be to have a "quality" choice in the Change Speed / Tempo / Pitch effects: High quality (slow) or Standard Quality (fast), where High Quality is the default.
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kozikowski
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Re: Change tempo without changing pitch

Post by kozikowski » Tue Mar 31, 2015 12:52 am

Different from what we have now. +1
Koz

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