Freesound Forums
phase shift
Started May 13th, 2006 · 7 replies · Latest reply by Bram 18 years, 6 months ago
Hi Guys,
Can anyone tell me how to phase shift a sound?. I need to create some software which will initialy shift some audio by 90degrees (andother values later), but i've got no idea how to go about it. I've looked on the web and it gets into quite deep maths quite quicky !. I've got a fair understanding of how the samples work in a .wav file and I code in C so I can get to the raw bytes with no problem.
I'd be very graetfull for any pointers
Regards
Kevin
this isn't a math answer, but a good way of thinking of it:
If you have two of the same waves it will double the amplitude (if played at the same time, and with the same speaker source... or complimentary speaker source).
If you have two signals that are completely opposite in amplitude you have perfect cancellation and no sound comes out. This is signal inversion and is commonly used to create stereo images for M-S imaging.
So, phasing exists somewhere in between those two extremes.
My guess is that if you take a signal and split it, you should be able to invert one, bump the Dbs down by 10 on one and remix the two. That should give you a simple phase effect.
also...
when you think of "phasing" effects for like guitars, its actually just a signal that is split, one staying clean, the other having a sweepable High Q applied to it, and then mixed back together. Sometimes you can invert one of the signals two, to create even truer phasing.
Again, i have never actually created programs for phasing, or tested what i have said above. I think i am correct in my reasoning though.
hope this helps.
oh, i actually left out an important step.
Wave inversion is an important part, but specifically phase shirft comes from the lack on alignment in either case (double or negation of the wave form)...
Thus you may see the problem.
To move something "out of phase" means that you shift the starting point of the wave.
In a sine wave at 440 hz will react differantly to a 3 ms shift than a 5khz sine wave.
Thus, that is why you can get away with the High Q in guitar pedals.
What i forgot to mention is, In a complex wave form "90 degree phase" sort of looses its meaning.
A more accurate way of stating the phase shift would be "90 degree phase shift @ 440 hz (or whatever frequency you choose... a sweepable phaser)...
cool. Glad i cleared that up (i hope)
in Logic 7.0 you have a 'Bit Shifter', with that you can delay one (or both) of the Stereo-Channels of an Audio-File
