Making high-fidelity audio sound like it came through the phone (2018)

There's a great plugin called "Engineer's Filter" which can do some more classical filtering (Chebychev, Cauer) to really get that vintage sound.

Zero'ing an FFT bin is neat for the phase artifacts/time domain aliasing.

https://www.kvraudio.com/product/engineersfilter_by_rs_met

Depends on what you mean by “simple”. If you want a circuit you can build with one op-amp and some passives from some coefficients you have memorized, without simulating it first, you're probably going to go with a second order Butterworth or something and get that gentle roll-off you're talking about. But if you're using SciPy or Octave, you can synthesize a tenth-order elliptic IIR filter and apply it in three lines of code (to me that's “simple”), and it'll be pretty brickwallish.

It's true that you get more latency as you move to lower-phase-distortion IIR and zero-phase-distortion FIR filters. But that's not a reason to filter in the Fourier domain instead, because in the Fourier domain you get all the latency. If you can pay all the latency that way, you can eliminate the IIR phase distortion with filtfilt.

Similarly, ringing in your IIR filter is not a reason to go to the Fourier domain and start bashing bins to zero, because you get all the ringing that way: the Fourier-domain difference between your original signal and the transformed signal is a Fourier-domain impulse, whose inverse Fourier transform is a sinusoid that fills eternity.

Also, just to be clear, and you probably already know this, but ringing and phase distortion are two totally different phenomena.

Just a guess, but I imagine he's talking about how we've been taught certain context clues from media that aren't exactly accurate. For instance, that bubbly low passed sound when a character is underwater or the crunchy punch sounds that aren't what a real fight sounds like.

> What's exactly the difference between the memory and emotion and the real sound of a telephone call?

When mixing a song, one of the many things to consider is, if a specific part is intended to blend in with other parts, effectively creating a merged sound vs. which parts are supposed to stand out. Since I use the telephone effect to make a part stand out a little extra, it becomes more important for it to be focused in a frequency range not already crowded with other parts. And therefore it’s less important if the highlighted frequency is a precise match to a telephone line.

> Do you have this kind of approach with other sounds as well?

Yes, very much so. For example in a very full pop or electronica mix with many parts, a grand piano track can overwhelm and muddy too many frequencies used by other instruments - for example the very low end (left side) of a good grand piano occupies the same frequencies as a bass guitar, upright bass or synth bass. So typically I would make the piano track be less prominent in the competing range, by lowering the EQ settings in that range. And I might increase the EQ settings for the frequency range where I want the piano track to me most obvious to the listener.

— There are fancier versions of that mixing technique via variable multi-band compression with side chaining, but that might go beyond the interest level of the HN audience and take this thread too far off-topic :-)

A fun thing with LPC is the lpc10 codec built into Sox, making it trivially easy to play with and get a very pleasing distortion.