[FFmpeg-devel] [PATCH 1/2] Add biquad high-pass and low-pass IIR filters.

[Måns Rullgård]

"Ronald S. Bultje" <rsbultje at gmail.com> writes:

> Hi,
>
> On Thu, Jan 20, 2011 at 4:26 PM, Justin Ruggles
> <justin.ruggles at gmail.com> wrote:
>> ---
>> ?libavcodec/iirfilter.c | ? 50 ++++++++++++++++++++++++++++++++++++++++++++++++
>> ?libavcodec/iirfilter.h | ? ?1 +
>> ?2 files changed, 51 insertions(+), 0 deletions(-)
> [..]
>> +    a0 = 1.0 + (sin_w0 / 2.0);
>> +
>> +    if (filt_mode == FF_FILTER_MODE_HIGHPASS) {
>> +        c->gain  =  ((1.0 + cos_w0) / 2.0)  / a0;
>> +        x0       = (-(1.0 + cos_w0))        / a0;
>> +        x1       =  ((1.0 + cos_w0) / 2.0)  / a0;
>> +    } else { // FF_FILTER_MODE_LOWPASS
>> +        c->gain  =  ((1.0 - cos_w0) / 2.0)  / a0;
>> +        x0       =   (1.0 - cos_w0)         / a0;
>> +        x1       =  ((1.0 - cos_w0) / 2.0)  / a0;
>> +    }
>> +    c->cy[0] =  (2.0 *  cos_w0)        / a0;
>> +    c->cy[1] = (-1.0 + (sin_w0 / 2.0)) / a0;
>> +
>> +    // divide by gain to make the x coeffs integers.
>> +    // during filtering, the delay state will include the gain multiplication
>> +    c->cx[0] = lrintf(x0 / c->gain);
>> +    c->cx[1] = lrintf(x1 / c->gain);
>> +    c->cy[0] /= c->gain;
>> +    c->cy[1] /= c->gain;
>
> Patch is fine.

Queued.

-- 
M?ns Rullg?rd
mans at mansr.com