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Why do mismatched sampling rates cause pitch/tempo issues??
Old 7th February 2013
  #1
Gear Maniac
 
🎧 10 years
Why do mismatched sampling rates cause pitch/tempo issues??

I'm sure this is a dumb question, but I can't find a good explanation by searching.

I understand the concept of why a higher sample rate creates a better fidelity recording (taking more snapshots per second to eliminate the staircase effect etc), but I don't understand the technicalities of why mismatched sample rates can cause pitch/tempo problems and not just a mere fidelity difference.

If I have a track in Pro Tools and bounce a 44.1 and a 48kHz version, they will both be the same length, so why do mixing and matching 44.1 and 48kHz files create these problems?

If anyone has the patience to help address my ignorance, I'd really appreciate it!
Old 7th February 2013
  #2
Lives for gear
 
1 Review written
🎧 10 years
Well, its simple,... really, ....if you have for example a file with a samplerate of 10 hz and one of 20 hz. The one of 20 hz played in a session set at 10 hz will be half speed and an octave lower. Get it...? It is samples per second....... Now do the math for the 44.1 khz and the 48 khz files.
Old 7th February 2013
  #3
Lives for gear
 
Ain't Nobody's Avatar
 
🎧 10 years
The issue with mixing and matching them is if they aren't converting in the process.

Your session will be set to one or the other. If the one that didn't match was converted first to match the session, there would be no pitch or time shift. If it's just playing sample per sample along with the session, however, it has more or less samples per second than the session, so it's essentially like playing a tape that much faster or slower.

Solution: Convert everything to the SR that matches your session. Not sure if that can be done on the fly in protools or not. may require conversion beforehand or checkbox when opening session or something. Logic guy here.
Old 7th February 2013
  #4
Gear Nut
 
audioexmachina's Avatar
 
🎧 5 years
Quote:
Originally Posted by hauntedclutter ➡️
I'm sure this is a dumb question, but I can't find a good explanation by searching.

I understand the concept of why a higher sample rate creates a better fidelity recording (taking more snapshots per second to eliminate the staircase effect etc), but I don't understand the technicalities of why mismatched sample rates can cause pitch/tempo problems and not just a mere fidelity difference.

If I have a track in Pro Tools and bounce a 44.1 and a 48kHz version, they will both be the same length, so why do mixing and matching 44.1 and 48kHz files create these problems?

If anyone has the patience to help address my ignorance, I'd really appreciate it!
Not a dumb question. Your 44.1 and 48 tracks will play exactly in sync as long as you use two separate D/A converters, one clocked at 44.1 and the other one at 48...

IF you run both tracks through a single converter (clocked at either 44.1 or 48) you get one track playing fine (the one with the same clock as the converter) and the other one playing at the wrong speed and wrongly pitched (think about the speed control of a turntable).
Old 7th February 2013
  #5
Lives for gear
 
timtoonz's Avatar
 
🎧 15 years
Not much different than what happens (or used to happen in the old school world) when you record on tape at 7 1/2 ips and then play back at 15... Tempo doubled, pitch doubled, etc... Or shooting video at 60 frames per second and playing back at 30-- slow mo.

Ah, the simple old timey days when 'sample rate conversion' was just a glimmer in a geek's calculator....
Old 7th February 2013
  #6
Gear Addict
 
🎧 10 years
Quote:
Originally Posted by hauntedclutter ➡️
I understand the concept of why a higher sample rate creates a better fidelity recording (taking more snapshots per second to eliminate the staircase effect etc)
Just to clarify though, the staircase effect doesn't affect your sound. Higher sample rates above 44.1 only increase the amount of treble in the recording. That increase being inaudible, btw.

The staircasing effect is smoothed out by your filters, you don't hear it, and it doesn't come through your speakers.

Just letting you know, as I used to have the same misconception.
Old 8th February 2013 | Show parent
  #7
Gear Nut
 
audioexmachina's Avatar
 
🎧 5 years
Quote:
Originally Posted by musichascolors ➡️
Just to clarify though, the staircase effect doesn't affect your sound. Higher sample rates above 44.1 only increase the amount of treble in the recording. That increase being inaudible, btw.
Yes, it's true that there's no staircase effect (heard several pros victims of this misunderstanding), due to the (required!) low pass filter applied when converting to analog. Actually the reason for recording above 44.1 isn't getting more trebles (which is also a correct statement) but rather making easier to build the required low pass cited above.

Assume you're done with trebles up to, say, 20KHz. If you record at 44.1KHz you need a very steep low pass filter with a very narrow transition band, from all-pass at 20KHz to all-stop at 22050Hz (half of 44.1KHz). Instead, if you record at, say, 96KHz, you are fine with a much gentler low pass with a transition band from 20KHz to 48000Hz (half of 96KHz).

In general a steeper filter means higher computational costs (more FIR coefficients).

Note that, beside filter complexity, the steeper one causes a sharper rotation of phase in the transition area.
Old 26th August 2020
  #8
Here for the gear
 
About Sample Rate and Pitch/Time on Pro Tools

Hi there, this is a topic that can be a little bit confusing but I'll try to explain it as simple as I can.
I'm not going to talk about the differences between recording or exporting at different sample rates, that's another subject. This is about the playback on Pro Tools and the relation between SR and Pitch/Time. Cut to the chase.

If we have a session set at 96kHz and we drag a file with a sample rate of 44.1kHz two things can happen. One: nothing. Two: It sound faster and with higher pitch. But why?
This is because of a configuration. If we go to Setup->Preferences->Processing. There is a box that says "Don't convert Sample Rate on import". If this is not checked, then Pro Tools will automatically convert any audio imported/dragged to the session. So you won't have pitch or time problems. On the other hand, if this is checked, PT won't convert it automatically. So there are 2 ways to proceed when importing a file:

A. You go to file-> import->audio . It opens a window where you choose the audio file and if it's on a different sample rate, you can click the option to convert it. (cleanest way to work).

B. You drag the file, it doesn't automatically convert (because the option in the menu was checked) so it mantains original SR. If the session is at 96kHz and the audio file at 44.1kHz, it will get smaller, faster and with higher pitch. What happened?

The PT is "counting" as the session is setup. This is 96kHz samples per sec and you gave it only 44.1kHz (less than half), so it need to "compress" the audio file to get those 96. If we do the opposite, have a session setup at 44.1kHz and drag and audio file of 88.2kHz for example, Pro tools will try to "count/read/playback" the 44.1kHz that is setup on the session. In order to do it, the audio file will get larger, slower and with lower pitch.

I'm attaching the screenshots of both examples so you can check it out. Notice that the track above is the one that has been dragged (as the option B and the menu box checked) and the one below is the original that was imported through previous conversion (as the option A). This is the one that plays and sounds like the original. The other is messed up (unless you want it that way for creative reasons. It's also something fun to try). I always leave that box unchecked so if I drag some audio file, it will automatically convert it to the SR of my session without asking (Pro Tools 12.5).

Hope this makes some sense and result useful for somebody. Cheers from Perú!

Pd. Also check the dynamic, one is "House of Cards - Radiohead", and the other is the "Chromatic Fantasia and Fugue in D minor - Bach". Guess which one haha.
Attached Thumbnails
Why do mismatched sampling rates cause pitch/tempo issues??-captura-de-pantalla-2020-08-25-la-s-17.30.47.jpg   Why do mismatched sampling rates cause pitch/tempo issues??-captura-de-pantalla-2020-08-25-la-s-17.29.58.jpg   Why do mismatched sampling rates cause pitch/tempo issues??-captura-de-pantalla-2020-08-25-la-s-17.30.24.jpg  
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