3 ms·

Impulse response is sort of overkill here. If you design a filter bank in the first place, you can just implement that filter bank much cheaper than doing even

Impulse response is sort of overkill here. If you design a filter bank in the first place, you can just implement that filter bank much cheaper than doing even an FFT-based convolution. Convolution is useful when you don't know the underlying filter transfer function.

cycomanic 2y ago
I'm not sure I understand. How would you apply your FIR filter? Are you suggesting there is a different way than to either do convolution in the time domain or a multiplication in the frequency domain?
- colanderman 2y ago
  Presumably GP is suggesting IIR filters?
- manawyrm 2y ago
  REW can generate a set of peaking/shelf equalizer filters, but why would I want to do that instead of just applying the inverse impulse response instead? It's just more work for a less perfect solution/result...
Retr0id 2y ago
> Convolution is useful when you don't know the underlying filter transfer function But we don't?
smj-edison 2y ago
Perhaps it's simpler to configure with a single impulse response vs multiple filters?
gmueckl 2y ago
This depends entirely on the length of the impulse response, doesn't it? A very short time domain convolution isn't actually more computationally expensive than a bank of crossover filters.
Sesse__ 2y ago
It really depends on what your filter bank looks like. If it's a 4-band parametric EQ, then sure, you can have four biquad IIR filters and that's it. But if you've measured an impulse response and want its inverse (e.g. through a Wiener filter), that's not what you have; you simply have another impulse response (effectively closer to a N-band graphical EQ where N >= 100), not a parametric EQ. As a nitpick: You always know the filter transfer function, it's the DFT of the impulse response (and without the impulse response, you obviously cannot convolve).
- thrtythreeforty 2y ago
  Agreed - I read this bit in the article: > generating a filter curve for a 300Hz slope, both channels were divided (A/B) against that curve as defining a parametric EQ band. If you just generally want to invert a measured impulse response, then yeah, you don't know the underlying transfer function.
  - Sesse__ 2y ago
    Well, immediately after that, they say they inverted the entire curve (through a naïve 1/|X| and then un-FFT, presumably) and saved it as an impulse response. I think the 300Hz slope is to _keep_ the rolloff in that area, so that the system doesn't try to boost bass by 40 dB and just end up clipping madly. Since these operations sort-of commute, it is easier to understand if you invert the order of operations: 1. Invert the spectrum (ideally through something less sensitive to noise than what's done here). Now you have an impulse response that will, in theory, give you a perfectly flat frequency response. 2. Apply a 300 Hz slope. Now you gave up some of that flatness, but you have something that's physically realizable without murdering your speakers.
    - manawyrm 2y ago
      Exactly correct, that was my thought process while doing it. I tried it without that 300 Hz slope first of course, but that did try to murder my speakers. :)
    - thrtythreeforty 2y ago

cycomanic 2y ago

I'm not sure I understand. How would you apply your FIR filter? Are you suggesting there is a different way than to either do convolution in the time domain or a multiplication in the frequency domain?

colanderman 2y ago
Presumably GP is suggesting IIR filters?
manawyrm 2y ago
REW can generate a set of peaking/shelf equalizer filters, but why would I want to do that instead of just applying the inverse impulse response instead? It's just more work for a less perfect solution/result...

Retr0id 2y ago

> Convolution is useful when you don't know the underlying filter transfer function But we don't?

smj-edison 2y ago

Perhaps it's simpler to configure with a single impulse response vs multiple filters?

gmueckl 2y ago

This depends entirely on the length of the impulse response, doesn't it? A very short time domain convolution isn't actually more computationally expensive than a bank of crossover filters.

Sesse__ 2y ago

It really depends on what your filter bank looks like. If it's a 4-band parametric EQ, then sure, you can have four biquad IIR filters and that's it. But if you've measured an impulse response and want its inverse (e.g. through a Wiener filter), that's not what you have; you simply have another impulse response (effectively closer to a N-band graphical EQ where N >= 100), not a parametric EQ. As a nitpick: You always know the filter transfer function, it's the DFT of the impulse response (and without the impulse response, you obviously cannot convolve).

thrtythreeforty 2y ago
Agreed - I read this bit in the article: > generating a filter curve for a 300Hz slope, both channels were divided (A/B) against that curve as defining a parametric EQ band. If you just generally want to invert a measured impulse response, then yeah, you don't know the underlying transfer function.
- Sesse__ 2y ago
  Well, immediately after that, they say they inverted the entire curve (through a naïve 1/|X| and then un-FFT, presumably) and saved it as an impulse response. I think the 300Hz slope is to _keep_ the rolloff in that area, so that the system doesn't try to boost bass by 40 dB and just end up clipping madly. Since these operations sort-of commute, it is easier to understand if you invert the order of operations: 1. Invert the spectrum (ideally through something less sensitive to noise than what's done here). Now you have an impulse response that will, in theory, give you a perfectly flat frequency response. 2. Apply a 300 Hz slope. Now you gave up some of that flatness, but you have something that's physically realizable without murdering your speakers.
  - manawyrm 2y ago
    Exactly correct, that was my thought process while doing it. I tried it without that 300 Hz slope first of course, but that did try to murder my speakers. :)
  - thrtythreeforty 2y ago