[PD] making puredata headphone-safe

[Simon Wise]

On 30/08/11 00:31, Hans-Christoph Steiner wrote:
>
> On Aug 29, 2011, at 12:19 PM, 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?
>>
>> Martin
>>
>> "If it seems like magic your assumptions are wrong." Martin Peach
>
> I am taking a biologist's approach here: I've observed this happening multiple
> times in the wild, now I have to figure out why. Its very reproducible, I've
> taken the field mice into the lab and seen them reproduce ;) Take Ed Kelly's fun
> LPC cross-synth example, in ekext/examples/lpc-cross-synthesis.pd. Put some loud
> samples into it and go crazy with the parameters and... MELTDOWN! I've never
> heard my computer make a louder sound... I knew that this patch has some
> feedback aspect to it, so I was doing my standard practice, having the volume
> very low.

Hmm - of course there is NO volume control on those headphones at all.

The volume is permanently set to full. When you turn down the level for 
headphones on the laptop you are only dividing the digital level (which must 
still be a float at this stage, given your observations) by some figure so that 
the DAC gets lower numbers. Then if pd is putting out much higher levels than 1 
they is never clipped until after! the headphone level control. The only way to 
keep the volume down is a limiter, compressor or clipper in your patch before 
[dac~], or feed pd into a limiter via jack before the headphones get it.


Simon