[PD] db and pd

[Marc Lavallée]

Le 22 Mai 2005 16:58, Roman Haefeli a écrit :
> hi marc
>
> Marc Lavallée wrote:
> > I understand now. Thanks!  But midi-dB resolution (1dB) is much too
>
> small;
>
> > interpolation is required to smooth volume transitions from the lowest
> > possible value to a certain level of amplification.
>
> what do you mean by 'too small'? our ears hardly hear the difference of
> 1dB. from that point of view, 127 steps are enough. 

In the good old days when MIDI was hot, I remembered hearing the steps when 
changing the volume rapidly with a MIDI fader. Maybe I was hearing the 
difference between a few consecutive steps instead of each steps. I was 
using consumer-grade equipment, the maximum volume was too high, and I 
don't know if the scale was linear or logarithmic... 

With midi-dB, as explained by IOhannes, the useful range is 0-100, the last 
27 steps are reserved to apply some amplification. With 127 steps instead 
of 100, it gives more precision. I agree that a fader with the full 
resolution of digital audio is useless, and that 127 steps is enough in 
most situations. I also use a 127 value slider to change the volume in my 
audio patches. But when modulating the amplitude of an audio signal with 
some control data, more rapidely than with a volume fader, 127 steps are 
not enough.

> on the other hand, 
> interpolation is needed anyway. it's not only a matter of the stepsize,
> but also of the time intervalls between different dB-values.
> depending on what interface (for example: guis in pd) you use, this
> intervall is too big, so that it's no way to use all steps of the scale.

Changing the volume smoothly with a low resolution fader works, and with 
good interpolation its perfect, but not too rapidly because the 
interpolation must measure the time between each steps.

> i usuallly use a square scale, which is somehow betweeen
> logaritmic and linear scale.

Interesting. 

> what is a good way? i mean, which scale is used by good mixers like
> neve? 

This article concludes that dBm (electrical power), not dB SPL (Sound 
Pressure Level, used by Miller) is the one used in the sound recording 
industry:
http://www.modernrecordingtechniques.com/about/excerpt.php

I guess it's only a matter of preferences...

--
Marc