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Lets say that I take chunks of signal S at a frequency F and I apply curve C accelaration of each chunk indepently so that each chunk starts whith the original speed and then fastens up (or down). Isn't that a phaser?

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  • If answers are still not what you want, it may help if you explain why you're actually looking for this effect - it may reveal the concept you're trying to explain, so we can better help you.
    – n00dles
    Commented Sep 13, 2022 at 7:32

2 Answers 2

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Flanging

Taking two signals from the same source, if one deviates in speed while the other stays constant, the peaks and troughs of the waveform interact with each other either cancelling or reinforcing each other in various ways. This can sometimes sound like you are listening through a tunnel or a drainpipe.

Phasing

Phasing is similar to flanging in that you are using one direct and one modified version of the same source audio.

However, with phasing, the peaks and troughs of the modified audio are artificially shifted out of phase compared to the original sound without changing the speed. This produces a similar sound to flanging but is usually much softer.

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  • I read about flanging, according to wikipedia, the modified signal is delayed/phase shifted, not accelerated or decelerated. May be that's another type of flanging? Commented Sep 8, 2022 at 18:25
  • If you're talking about slowing the sound down digitally without changing the pitch then you're achieving the same effect as a delay. If you're talking about changing the pitch too, then that would be detuning - similar to detuning two oscillators on a synth - you get a 'wider' sound. Commented Sep 8, 2022 at 20:52
  • ahh I can't tag you automatically. Indeed I was thinking of gradual acceleration (and treating the signal like chunks), so that t'=kt² which generates a chirp on one side and remixing with the original or even the signal with the opposite chirp. Like a fade in&fade out but with time instead of amplitude. Commented Sep 8, 2022 at 21:36
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I think you want a frequency-domain effect like frequency modulation.

I'm sure you know what frequency modulation is, well, if the modulator signal is a sawtooth wave, then you would get periodic rising and (ideally) instant resetting of the carrier frequency. The period would be equal to the modulator frequency/1. So a 1 Hz modulator frequency would reset the rising of the carrier frequency every second - this would be your "chunk". You can change the slope of the sawtooth wave to get an increasing or decreasing acceleration curve. The amplitude of the sawtooth would be known as deviation in Hz. i.e. Linear deviation from the carrier frequency.

Technically, a sawtooth wave would also lower the frequency of the carrier wave by deviation/2 Hz. So in order to begin and end the chunks at carrier frequency, you would need to raise the modulator's DC offset by deviation/2.

So then, with a carrier of 50 Hz, a modulator of 1 Hz with a deviation of 10 Hz, the carrier signal would rise for one second to 60 Hz then fall back to 50 Hz.

Here is a quick example of what I'm talking about, firstly using a parabolic sine wave as the carrier, then a (slightly down-shifted) song. (You may be able to hear the "speed" changes more clearly in the song):

https://on.soundcloud.com/KB57o

https://on.soundcloud.com/mTYdM

As a side note, Phasers are similar in a way, but they create (usually 1-~10) additional versions of the carrier signal, inverting the phase of some and slightly detuning them with a Low Frequency Oscillator (the modulator) to get a moving-effect as the multiple carrier signals fall in and out of phase with one another. I think it's too complicated for what you talk about.

This is an example of a phaser I recorded a while back:

https://soundcloud.com/n00dlz/phaser-example?si=7cdfedac2082466d9e257a8c7c572e4d&utm_source=clipboard&utm_medium=text&utm_campaign=social_sharing

As far as I can tell, simple FM is what you're referring to. I'm not a mathematician, so t'=kt² scrapes over my head :)

Note: I'm assuming by "speed", you mean cycles per second, i.e. frequency (frequency is inversely proportional to wavelength, which is the distance from one cycle to the next, so as the wave gets shorter, the frequency rises). When we talk about logarithmic frequency changes, we usually use the term "pitch" instead.

Useful Resources
FM on Wikipedia (General)
FM Definition on Heavy.AI (General)
FM Synthesis on Wikipedia (More relevant to sound synthesis)
SoS - Introduction to audio FM (Exclusively sound-based)

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  • I'm sad to tell you that you're totally wrong this time, you didn't take my analogy. I said like fade in/fade out but with time instead of amplitude, these means I'm affecting speed and not perceived volume, you get me now? I know what modulation is and it generally affects volume, your sawtooth effect is a clear example of a periodic fade in, but I'm not interested in that. In more simple words, I want an effect similar of that of the sawtooth but rather affecting speed not volume, so the sawtooth would be the speed in function of time instead of peak in function of time. Commented Sep 10, 2022 at 20:40
  • And btw I'm neither sure if t'=kt² but surely it would be a time map function like that Commented Sep 10, 2022 at 20:40
  • @LerianAcosenossa Hi Lerian. My answer does exactly that. I think you're thinking of Amplitude Modulation. This is Frequency Modulation. Frequency = "speed". Maybe I should have made it more clear. Would you like me to show you how it works? I'll knock up a quick example if you like.
    – n00dles
    Commented Sep 10, 2022 at 20:53
  • I'm not familiar with frequency modulation, but I suppose I understand the concept now, obviously is famous by its acrononymous FM, but I haven't saw that coming and I still don't see what multiplying frequencies has to do with the speed of the signal, theoritically you are only pitch shifting over periods of time but that shouldm't affect the time that a sound would show up, it would only make it sound lower and higher over time, what is a consequence of altering speed but not the main factor. Throw me an example, just in case. Commented Sep 10, 2022 at 21:10
  • @LerianAcosenossa I updated answer with some examples ;)
    – n00dles
    Commented Sep 11, 2022 at 0:35

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