how to change the hertz in GB?

I assume you mean the A440 tuning standard.

Garageband has no support for this. You can use pitch bending or some other techniques for simulating this, but it is a bit of a hack.

I am not sure what you mean by tuning the *mic* to various pitches, but something like Audacity can take a "real instrument" track and alter its pitch.

You can use the AUPitch effect on all your tracks to alter the pitch. You'll have to do some math:

E.g., if you want to play the piano with a 432 Hz tuning, you'll have to set the AUPitch (which goes in cents = 1/100 of a semitone) to minus 31 cents.

)Here's the math: one cent up is (2^(1/12))^0.01 = 1,00058 times the frequency. Divide the frequency by the same number to go one cent down. How many cents is it to go from 440 to 432 Hertz?

1,00058^x = 440/432 = 1,01851

x*log1,00058 = log1,01851

x = log1,01851/log 1,00058 = 31,63)

^ means to raise to a power, 3^2 is 3 squared, or 3*3.

log means the common base 10 logarithm function.

If you don't have a scientific calculator, google can do it for you.

but just use the -31 cents and you don't need to know the math.

I admit it's a bit hard to comprehend because frequencies don't go linear but exponentially - each octave doubles the frequency of a tone. So to go up one semitone (in an equal tuning), you have to multiply a frequency by the 12th root of 2 (or divide by this factor to go down one semitone). One cent is 1/100 of a semitone, so it's the 1200th root of 2. The calculation computes the number of cents you need to adjust from a 440 Hz to a 432 Hz tuning.

I have tried to use AUPitch to set each track (or also the Master track insted) to -31 cent.

But GarageBand (latest Version) insists to reset it to -24 cent! (after reopening the AUPitch) 😟

Any ideas why od how to change this?

Well, when I import a song into Audacity and there call the Apple AUPitch, this plugin works as it should and resamples to -31 cent. Just to let you know....

Ha! Found the mistake in GB!

The input into the AUPitch plugin is not being accepted, as long as the "Music keyboard" (Musik-Tastatur in German) is opend and visible. Closing it, everything works as it should, even with -31 cent. 🙂

Good, that we talked about it! 😝