Re: [linux-audio-dev] applying RIAA curves in software

On Tue, Oct 25, 2005 at 08:38:18AM -0500, Richard Smith wrote:

> I haven't found any RIAA filters yet so I guess I'm looking at
> writeing one. So does anyone have any information on where to find
> the official RIAA curve to make a plugin from?

The curve as used in most preamps is the combination of
two filtering operations:

- a -6dB / octave filter (i.e. integrator) to compensate for
  the velocity response of a magnetic pickup,

- the real RIAA curve.

Combining the two gives a filter like this:

(use a monospaced font to view this)

______
      \
       \
        \__________
                   \
                    \
                     \
                      \
         
The corners are at 50, 500, and 2120 Hz IIRC.
Slope is -6dB / octave, so the weighted sum of two
first order lowpass filters is all you need.

-- 
FA