Help! 44.1 VS 48.0 = changed pitch in Simpler, Granulator...

[rutgermuller]

Usually I make all my projects in 48.0KHz. For one project I accidentally worked in 44.1KHz. Now when working in that project I have to switch Live to 44.1KHz all the time, because leaving it on 48.0 messes up some glitch sounds I created with Simpler and a very short loop region. (This goes for using either my MOTU or my internal MacBook Pro audio)

The strangest thing is that when I stay in 48.0KHz, and I freeze the Simpler track, it suddenly sounds good! While the freeze/bounce is 44.1 not 48.0. But then I have to freeze and unfreeze the track all the time to make MIDI changes....

So is there a problem with the real-time sample rate conversion in Live?

[swishniak]

not sure what you mean by "sounds good." you mean it plays back at 44 or 48?

[timday]

Are you using Redux at all? I ask because it's a glitch sound. If you're using Redux to downsample, the alias tones created from a 48HKz sample will not be the same as the ones created from a 44.1 KHz sample because the alias frequencies depend partially on the sample rate.

The other thing that occurs to me - and I'm speculating here - is that maybe Simpler's minimum loop size is based on number of samples rather than mins/seconds. If you are down at the minimum then changing SR would then actually change the length of the loop (going from 44.1 to 48 KHz would shorten it) which might make a difference.

[rutgermuller]

It's just a Simpler I'm using.

After some Facebook discussion we concluded that it's probably the rounding errors in Simpler, those get corrected when freezing a track, but not before...

"Wouter Snoei: Do I understatement correctly that your fast loops are sounding at a different pitch in 44.1 than 48, unless you freeze the track and play it in your 44.1 session? If so it could be explained by rounding errors; if the loop is <n> samples long in 48, and you convert it to 44.1 it will have a different length which is not necessarily a round number. However a sampler can only loop on whole samples. That could explain a pitch difference in the result. Then if you would render the whole track in 48k and then convert to 44.1 (which is probably what ableton does) there is no problem as the loop length induced pitch is already created.


Rutger Muller: Correct. I think it's the pitch. I'm just surprised that real-time sounds different than rendered. How is that ok?


Wouter Snoei: the trick is to know when the conversion takes place. For example; if your loop is 8 samples long in 48K, it would create an audible base frequency of 6000Hz. Now, if I convert the loop itself to 44.1, it would get a new length of 7.35 samples. Since there is no such thing as a partial sample this would probably be rounded to 7 samples, which would result in a base frequency of 6300Hz. This 300Hz difference would most definitely be audible. But that doesn't mean that every 6000Hz frequency in 48 becomes 6300Hz in 44.1; sample rate conversion uses interpolation (which is all about partial samples) to convert all frequencies correctly, and if you render the 8 samples long loop in 48k and then convert the rendered track into 44.1 you will actually hear the 7.35 samples long loop, re-calculated to fit on whole samples. That's the magic of interpolation for you . This is not a mistake of Ableton, it is simply a result of sampling theory. Btw longer loops will have lower rounding errors, which may be why this problem only pops up at really short loops. If programmed well a sampler could actually do the interpolation internally, but indeed I think the makers of Simpler would consider this a corner case.


Rutger Muller: Ah, so freezing the track takes the sound you hear, and throws it through an additional conversion?



Wouter Snoei: I suspect so"

I'm not very happy with this, but I'll just use the freeze workaround and in the future run all projects on 48.

[rutgermuller]

I just found out that this is even a bigger problem when using Granulator II,
in my case 48.0 sounds two semitones higher than 44.1


So it is really necessary to remember in which Sample Rate Ableton was set when you made a project, right?

[rutgermuller]

nobody wants to geek out about this?