[LAD] Re: EQ Matching

Hi Fons,

thanks for your comments! Sorry for replying so late ;)

On 5/21/2023 11:24 AM, Fons Adriaensen wrote:
> On Sat, May 20, 2023 at 05:15:03PM +0200, Florian Paul Schmidt wrote:
>
>> 1. Are there any glaring oversights with this approach?
>
> The minimum phase step is not really necessary, you could just use the
> linear phase version, the output of the IFFT rotated by half its size.

Yeah, I want to use this in a real-time context though, so the initial
delay in the linear-phase version is non-acceptable.

> If you do the minphase operation, the best way to do this using an FFT
> that is at least 4 times as long as your IR. In other words, take the
> linear phase version in the time domain, add zeros, then do the
> minphase calculation.

Yeah, I will try and incorporate that!

> This probably should not depend on the absolute values, just on the
> ratio, i.e. the calculated gain. If r = s2 / s1 you could impose a
> smooth maximum:
>
> g = r / sqrt (1 + M * r * r)    with M in the range 1e-3 to 1e-2
>
> Or you could even reduce the gain if r is really very high (which
> probably means there is nothing of value in s1 at that frequency:
>
> g = r / (1 + M * r * r * r)     with M in range 1e-5 to 1e-4
>
> Try this in gnuplot:
>
> plot [0:100] x / sqrt (1 + 1e-2 * x * x), x / sqrt (1 + 1e-3 * x * x)
> plot [0:100] x / (1 + 1e-4 * x * x * x), x / (1 + 1e-5 * x * x * x)
>
> to get an idea of what these will do.

Looks good!

> Average levels in the two input files should be more or less
> matched, before applying any of these.

Couldn't I just compute the sum of the squares of the fft bins to get
the total energy in both s1 and s2 and normalize both to e.g. 1?

Kind regards,
FPS

--
https://dfdx.eu
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