[PD] making puredata headphone-safe

[Roman Haefeli]

On Mon, 2011-08-29 at 12:19 -0400, Martin Peach wrote:
> On 2011-08-29 11:52, Hans-Christoph Steiner wrote:
> >
> > On Aug 23, 2011, at 3:43 PM, Martin wrote:
> >
> >> On 23/08/11 03:29 PM, Stephen Lavelle wrote:
> >>> I've managed to hurt my ears twice over the past two days when using
> >>> PD w/ headphones. Even at lowest system volumes, it seems that
> >>> Terrible Things can happen. Are there any precautions that I can take
> >>> to make it feel less like I'm taking my life into my hands when I
> >>> have to use headphones?
> >>>
> >>>
> >>>
> >>
> >> Try making a [noise~] connected directly to a [dac~] and set the
> >> headphone volume so you can live with that. Nothing will ever be
> >> louder than that.
> >
> >
> > Hmm, I don't think that's actually true in all cases. On a MacBook Pro
> > running Mac OS X, I've had the volume set to one above mute, but had
> > massive feedback from LPC patches that were very very loud. [noise~]
> > would be very comfortable at that volume setting. I think some platforms
> > do the output mixing in the digital domain, so my min volume would be
> > [*~ 0.01], so that this would still make a very loud sound:
> >
> > [noise~]
> > |
> > [*~ 999999]
> > |
> > [*~ 0.01] (i.e. the Apple output mixing)
> > |
> >
> > In this particular case, the sound output actually gets shutdown
> > entirely, so you have to reboot to get sound output again.
> >
> 
> That make no sense. How can you have two sounds at the same level going 
> into a mixer that come out at different levels? Or do you mean that a 
> squealing sound is perceived to be louder than white noise? Maybe you 
> could demonstrate with a patch?
> 

I always had the feeling, that on OS X on MacBooks (Pro) the sound
coming from the speakers is heavily processed. Audio sounds a lot
'punchier' than for example the same audio played on the same machine
from Linux. I haven't had a chance to play around with it, since I don't
own a MacBook, but from what Hans says, to me it sounds as the
application output is not clipped to -1/1 before going to the (CoreAudio
internal?) dynamics stage, but processed and limited first and only then
sent to the speakers. This would also explain, why the setup Hans
explained above would completely shutdown the sound output.  Probably,
if you wait long enough, sound would come back again, assuming that it's
the limiter's release time, that becomes very long due to the very high
level coming in...   

just my 2¢

Roman