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Topic: How to shift entire audiofile by 24kHz (Read 2431 times) previous topic - next topic
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How to shift entire audiofile by 24kHz

Hi all,

I like to shift the whole audioband by 24kHz.
e.g. 20Hz will be 24020 Hz, 1000Hz will be 25000Hz etc.

My point is to shift a whole audioband 0-24kHz to 24kHz-48kHz. (0-24kHz will be silent and the music is at 24kHz-48kHz).

How to manage this? SoX? Any other tool?

Best,
.halverhahn
.halverhahn

Re: How to shift entire audiofile by 24kHz

Reply #1 –
Generally, no.   A "linear" frequency shift is multiplication (re-sampling) which means if 24020Hz is doubled to 44,100Hz then 20Hz is doubled to 40Hz.

It could probably be done using FFT (actually DFT) and writing a custom program, or with MATLAB, etc.

Re: How to shift entire audiofile by 24kHz

Reply #2 –
Do a sample by sample multiplication with cos(2*pi*24000*t). 

The sampling rate must be at least 2x the highest frequency present after the multiplication, so be sure to resample first.  96k is a good choice for normal audio.

Re: How to shift entire audiofile by 24kHz

Reply #3 –
MusicScope has Frequency Translation tool but it works the other way around - it lets you shift a band of high frequencies to 0-X kHz.

Re: How to shift entire audiofile by 24kHz

Reply #4 –
Quote from: saratoga on
Do a sample by sample multiplication with cos(2*pi*24000*t). 

The sampling rate must be at least 2x the highest frequency present after the multiplication, so be sure to resample first.  96k is a good choice for normal audio.
It would be good to mention that a high pass filter with a passband of 24kHz and above is necessary after this procedure. Also, this method doesn't work when the bandwidth of the shifted signal and that of the original signal have a common frequency band.

A more general way of doing this would be using the Short Time Fourier Transform with overlapping, moving the audioband frequency coefficients to the desired band, and then IDFT-ing them and adding them back together. Like DVDdoug said, it can be done by writing a program.

Re: How to shift entire audiofile by 24kHz

Reply #5 –
You would think this should be easy operation :)
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Re: How to shift entire audiofile by 24kHz

Reply #6 –
Hi, back in analogue times this was done with a frequency mixer.
Maybe you can simulate a ring modulator by software?

Re: How to shift entire audiofile by 24kHz

Reply #7 –
Quote
You would think this should be easy operation
I think it's the nature of frequency....  cycles per second.  There's a numerator and denominator.

I was trying to think of an analogy...  Imagine you have two cars going-around a race track.   One makes 100 laps per minute and the other 200 laps per minute.    If we make the track shorter (or speed-up the film) so the 1st one makes 101 laps, now the faster one now makes 202 laps, not 201 laps.  

Re: How to shift entire audiofile by 24kHz

Reply #8 –
Quote from: Sunhillow on
Hi, back in analogue times this was done with a frequency mixer.
Maybe you can simulate a ring modulator by software?

The term is frequency shifter - which is different from, but sometimes confused with a pitch shifter. It is related to a ring mod. A ring mod produces both sum and difference frequencies and suppresses the original signal whereas a frequency shifter breaks the sum frequencies and difference frequencies out separately.

Re: How to shift entire audiofile by 24kHz

Reply #9 –
It's actually quite a transformation, kinda like mapping a sphere to a part of a bigger sphere's surface... You squeeze inherently exponential frequency domain into more linear scale... If you could hear such processed audio, it would be all altered and detuned.