audio widgets etc, was Re: [linux-audio-dev] Is ladspa actually la-dsp-a? Is JACK the ultimate solution?

[Steve Harris]

On Wed, Jun 09, 2004 at 02:35:56PM +0100, Chris Cannam wrote:
> On Wednesday 09 Jun 2004 1:50 pm, Steve Harris wrote:
> > A little bit of meter standardisation wouldn't hurt - eg. the point
> > at which people show red seems to vary a lot, which has been
> > confusing for users.
> 
> Also is there a common convention for how dB levels map to positions 
> on a fader or meter?

Yes, IEC-268:

float iec_scale(float db)
{
    float def = 0.0f;           /* Meter deflection %age */

    if (db < -70.0f) {
        def = 0.0f;
    } else if (db < -60.0f) {
        def = (db + 70.0f) * 0.25f;
    } else if (db < -50.0f) {
        def = (db + 60.0f) * 0.5f + 5.0f;
    } else if (db < -40.0f) {
        def = (db + 50.0f) * 0.75f + 7.5;
    } else if (db < -30.0f) {
        def = (db + 40.0f) * 1.5f + 15.0f;
    } else if (db < -20.0f) {
        def = (db + 30.0f) * 2.0f + 30.0f;
    } else {
        def = (db + 20.0f) * 2.5f + 50.0f;
    }

    return def;
}

It also defines which points you should mark on your scale.

- Steve