[PD] limiter questions

Derek Holzer derek at umatic.nl
Wed Aug 26 13:21:25 CEST 2009

Too reiterate, try translating the values you put into your patch 
between dB and RMS. dB is logarithmic while RMS is linear, so your 
absolute gain increase of 4 times the original signal translates to 112 
dB. 100 dB is the "clipping point", or a Pd signal level of "1", thus 4x 
the original signal is 12 dB over clipping. And your limiting threshold 
of 90 dB translates to a scaling factor of 0.316 times the original signal.

Confused? Want a picture?


(Source: http://www.phys.unsw.edu.au/jw/dB.html)

Where the author has written "power", think RMS. So twice the RMS value 
is an increase of +3 dB. Likewise, half the RMS values is -3 dB. Because 
you were calculating your limiter entirely in dB, the RMS values needed 
for correct limiting were all wrong (far too little) so it didn't appear 
that your limiter was limiting at all!


Derek Holzer wrote:
> But this one does. Working in RMS values appears to be the solution to 
> your problem.
> D.
> Mirko Maier wrote:
>> Thank you, but it definitely doesn't limit the signal!
>> -------- Original-Nachricht --------
>>> Datum: Wed, 26 Aug 2009 12:16:17 +0200
>>> Von: Derek Holzer <derek at umatic.nl>
>>> An: Mirko Maier <mirkom at gmx.de>
>>> CC: pd-list at iem.at
>>> Betreff: Re: [PD] limiter questions
>>> You may want to investigate the relationship between dB and RMS 
>>> further. Attached is a working patch, however very crudely. Have a 
>>> look at the numbers given by the [dbtorms] and [rmstodb] objects. 
>>> Note use of [line~] as well.

::: derek holzer ::: http://blog.myspace.com/macumbista ::: 
http://www.vimeo.com/macumbista :::
---Oblique Strategy # 26:
"Change ambiguities to specifics"

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