Jump to content

Finding the Exact Frequency of a Piece of Audio


fader8

Recommended Posts

I've had several requests about how to find the exact frequency of various bits of audio, namely things like the initial tuning of a drum, which can be very elusive for a spectrum analyzer or impossible for a tuner plug-in.

 

Here's how to do it and it's very simple!

 

In the Sample Editor's View menu, choose Min:Sec:Ms:

minsec.jpg.caa5d2bcbaeb189d2a572e9c2766dfc2.jpg

 

Zoom in on your sample enough to clearly see the waveform. Swipe to make a selection between consecutive zero crossings, as shown:

selection.jpg.b6629f7270ca524b3feeca3cd3270534.jpg

 

In the top right of the Sample Editor, the length of your selection is shown in milliseconds. In this case it's 6 msec, (.006 seconds).

6msec.jpg.40a3528f579e0b35d19a11cda204b51a.jpg

 

We would only ever select the full wavelength if we knew the signal was a constant pitch. If that were the case, we probably wouldn't need to do this exercise!

 

Since this selection is only one half of the wavelength, we need to double this time value to .012 seconds to determine the value in cycles per second (Hertz). Now open OSX's Calculator app and change the View preference to "Scientific".

viewsci.jpg.21646039fa80290c5b48cffea12beb91.jpg

 

Enter the wavelength duration and then click the "Inverse" key:

inverse.jpg.60258fb42fb479adee6b3a26761fb0cc.jpg

 

Presto! The frequency in Hertz of this kick's loudest fundamental is 83.3!

answer.jpg.eae7901ca3e2c4ae21782caecc68c1e8.jpg

 

That wasn't so hard, was it?

Cheers, fader8

Link to comment
Share on other sites

  • 2 weeks later...
How come you don't select the whole wavelength from the get go?

Because he wants to know the frequency of that very specific section, which is not the same as the frequency of the bit before.

 

Why double?

Because he's selecting only half a period.

 

and I'm asking to know if there's a difference?

Yes, there would be a difference since the length of the different half periods are not the same. Different wavelengths = different frequencies.

 

Just one question:

That was three questions.

:wink:

Link to comment
Share on other sites

Is there a way to find out the frequency range of an instrument throughout the song?

Use a spectrum analyzer on that track. If the analyzer has a "Slow" setting, use it. These things have better frequency resolution when they have more time to make their measurements.

Link to comment
Share on other sites

Thanks a lot! Does Logic Have a spectral analyzer? I had a look under Metering and then everywhere else but didn't find one. I found a Spectral Gate but that's obviously a gate.

If Logic doesn't have it, anywhere I can download one? (Freeware preferably, as I can't shop online)

 

Sorry for all the questions. I appreciate your time. :)

Link to comment
Share on other sites

  • 2 weeks later...
just to be clear though, do we sort of ''round it down'' to the nearest note if the frequency isn't exactly spot on ??

Depends on what you're doing, and the workflow. Generally speaking, you should just do what sounds good.

 

Also, how do you determine the note when you know the frequency? Is there a simple formula to memorize? :D

Nice little java calculator here for that:

http://www.phys.unsw.edu.au/music/note/

Gives you the note with plus or minus cents, which is useful for tuning the sample, or tuning a synth to the sample.

 

Or you can plug it into the calculator. The formula for equal tempered scales is here:

http://www.phy.mtu.edu/~suits/NoteFreqCalcs.html

Link to comment
Share on other sites

  • 2 months later...
  • 1 month later...
  • 7 months later...
  • 3 years later...
We would only ever select the full wavelength if we knew the signal was a constant pitch. If that were the case, we probably wouldn't need to do this exercise!

 

Since this selection is only one half of the wavelength, we need to double this time value to .012 seconds to determine the value in cycles per second (Hertz). Now open OSX's Calculator app and change the View preference to "Scientific"

 

I don't get this at all... How is it half a wave length? When clearly it's only about 1/12th of the full wave length?

Link to comment
Share on other sites

Here's the definition of wave length:

 

waveform.png

 

Where to do you get 1/12th from?

 

Gee, thanks for all your help! He mentions that he had to double his 0.06 wave length because it's only 'half a wave length' + each wave in my kick is of different length, so therefore is my kick in lots of different keys?

 

Thanks for helping this n00b learn!

Link to comment
Share on other sites

  • 2 months later...
Speakers work by moving rapidly out/in to make a wave form.. So they start at a mid point (as 0 volts ) and then move out (as a + voltage, and in (as a - voltage), to make the the first cycle.. It is this pushing and pulling of cone which makes the sound. Once the cycle starts moving above 16 - 20 cycles a second we begin to discern a pitch.. Middle A is the waveform crossing 0 volts 440 times a second. Faster and slower waveform crossings either above 0 volts, or below 0 volts will color the pitch (harmonics), otherwise a perfectly symmetrical wave form (out/in) would be a sine. I believe you need to look at the plus and minus voltage of the wave form to determine it's pitch properly. If you look at the first wave form you'll notice the above 0 volts is shorter in duration, then the minus voltage.. So doubling the below 0 voltage, is not going to give you an accurate viewpoint (rather earing point) of waveform cycle..
Link to comment
Share on other sites

  • 3 years later...
  • 1 year later...

The internet is full of hatred and ignorance...and then I find a thread like this where someone spends their time helping other musicians to make music and it gives me hope!

 

Thanks so much for this. Now all the other kids on my block won't make fun of my for having kick drums that are out of tune!!!

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...