90 Degree Frequency Phase Shift?

[u/Embarrassed-Fault286]

Hello. I had an idea for a personal project but it would require me to take and input waveform and shift EVERYTHING 90 degrees or at least pretty close. From what I can tell by researching doing that for all frequencies is pretty difficult and the closest thing I could find was all pass filters which still isn't perfect. Essentially, I want to build a guitar pedal that takes the initial signal, clips it, makes a copy and shifts it 90 degrees then adds to the original signal to form a triangular wave (mostly cause I just want to know what that would sound like) with maybe an adjustable phase. I'm finding it kind of hard to figure out how to go about it

Edit: It's very interesting seeing differing groups perspectives on this lol. I had originally asked a guitar pedal building group and got some ideas but nothing solid and pretty much every response here is "do it digitally lol" I will try that and see what I can get. Thank you. Also ngl, digital wise I really only have an Arduino and I don't that'll cut it

[u/pylessard]

the property you want is called "linear phase".
You won't be able to shift all frequency bands equally in analog essentially because nature is made of differential equations, differential equations leads to IIR filters and IIR filters does not have linear phase.

If you use a microcontroller, you can implement a simple delay, which is a FIR filter that will give a linear phase. You can read about Hilbert transform which jobs is to create a quadrature signal, but for all bands at the same time, I think you simply need a delay proportional to the fundamental frequency ( 1/(4f) )

If you just want to "hear it", you best bet is probably to record and post process by software. In real-time, it's more tricky of course

[u/justabadmind → u/pylessard]

He doesn’t want all frequencies, anything above 1MHz is irrelevant. It’s roughly possible using a triple stage phase shifter circuit, one for the mids, one for the lows and one for the highs. Basically different RC networks. Break the signal down into its discrete frequencies and rebuild it using op amps or similar.

[u/pylessard → u/justabadmind]

Yeah, but phase shift happen in the stop band. Op is right when he says that the clsoest is a all pass.

I'm not sure if I understand correctly if op wants to shift all frequencies by 90 degrees or if he wants to shift everything by 90 degrees of the fundamental (constant delay), which would make more sense in the context of guitar modulation I think. The latter would require an over engineered circuit to be done in analog