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Re: Safety Switch

To Aaron and List,

        What you need is called a Limiter. This is a special form of a
compressor which remains linear in the majority of its (bipolar) range;
however, when the signal amplitude reaches higher thresholds, the Limiter
goes into extreme compression like 10:1 or 20:1. This means that signals
over the threshold which increase by a factor of 10 are translated to the
output as an increase of only 1 or 1/2, corresponding to 10:1 and 20:1
limiting ratios. Really hard limiters have an infinite limiting ratio.

        I just double checked and you can find out much more by searching on
the web, including some low-cost stereo analog limiters used for some FM
radio and other audio systems. Limiters are also sometimes used in the
recording studio.

I hope this helps, happy limiting!
Tom Maglione

-----Original Message-----
From: AUDITORY Research in Auditory Perception
[mailto:AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Aaron L Hastings
Sent: Thursday, March 03, 2005 11:42 AM
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: Safety Switch

Hello All,

I am wondering whether or not people include some type of safety switch
in their playback systems and if so what do they use?  We have a
playback system which consists of a LynxONE audio card, a TDT
attenuator, and Etymotic earphones.  We play sounds that are typically
as high as 70 dB SPL.  It is physically possible for our system to play
sounds greater than 90 dB and we would like to include a safegaurd so
that sounds sent to the attenuator, will not be played at levels greater
than XX dB.  Does anyone have any advice / experience with this issue.

Issues that I see at present:

    Anyting that we insert into the loop will increase noise

    A kill switch might also introduce a loud (damaging) noise depending
on how it is designed

   A compressor would introduce non-linearities and it may not be noticed
when it is actually affecting the signal and when not

Thanks for any input