linuxaudio.org

[Fons Adriaensen]

quoted text
>On Tue, Mar 19, 2013 at 03:02:19PM +0100, Tim Goetze wrote:

>> Surely you realise this version executes exactly as many additions and

>> multiplications per sample as a biquad?

>

>Yes. In this case it's possible to remove one multiplication:

>

>a = 0.07f;

>b = 1 + a;

>

>// ...

>

>gm = b * gt;

>for (i = 0; i < nframes; i++)

>{

>     g1 += w * (gm - g1 - a * g2);

>     g2 += w * (g1 - g2);

>     out [i] = g2 * in [i];

>}

Very nice work, it's lighter on state and setup, and now also on

execution.
Since this is not a highpass, let's just skip any claims of increased

stability.
However, I still take issue with the rather exaggerated claim that

using a biquad to smoothen gain changes would be "giant overkill".  It

may be slightly less efficient than your now optimised version, but

certainly not enough to substantiate this claim. 
In fact, I think this is a rather grandiloquent choice of words that

is entirely uncalled for.
BTW, at the cost of that one extra multiplication, the biquad is more

versatile if you run the gain filter permanently: you can simply feed

it the current knob value and it will automatically produce a nice,

smooth curve, without needing to be set up again for every gain

change.

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