In article <Bxnmf.41$pF.10@trndny08>,
Adam Stouffer <adam_stouffer@hotmail.com> wrote:
Quote:
Anyone have a schematic for something to limit the volume from line
level sources? I hate watching a tv show or movie and then getting
blasted by a commercial at twice the volume.
|
One attack of the problem:
Comparitor
LM311 Sign
--!>---------------------------------------------
! ------ !
! ------- ------ ! High ! ------- ---
In -----+--! ABS() !---! ln() !--! pass !---! exp() !---! X !-- Out
------- ------ ------ ------- ---
One advantage this has is that the ln() and exp() operations can be quite
well matched and tend to track with temperature. Also, the high pass can
have a few poles in it without stability problems.
Other method:
Any normal feedback based one, needs a quite linear multiplier to sound
any good. You may be able to take advantage of the fact that for normal
volume levels you don't want to change the sound at all. I'm thinking of
something like this:
Audio
quality
buffer
!\
-\/\/\---+---------! >-----------------+--------------- Out
! !/ !
! --------
! J1 U1 LM324 ish ! -ABS() !
--! /+!--GND --------
!<--+---< ! D1 R1 !
--! ! \-!--+-->!--/\/\--+
! ! ! R2 !
GND +---!!----+---/\/\/-----
C1 !
---/\/\-- +Vref
R3
The Jfet J1 is selected for having a high Vgs off.
D1 is a 1N914 like diode.
The output of U1 normally rests at the (-) supply rail. Op-amps like the
LN324 don't have diodes across their inputs so C1 will charge up to more
than just the rail voltage. Vref, R3, R2, D2 and R1 sets the amount of
"integrator wind up".
When someone shoots the bad guy, there is bang. If it isn't followed by
abunch more noise, R1 and D1 won't be able to discharge C1 far enough to
start the output of the LM324 going positive, so you won't effect the
sound.
When the soap ad comes on, The output of U1 (LM324) will swing positive
and reduce the sound. A fair bit of distortion will be added but you may
not care.
--
--
kensmith@rahul.net forging knowledge
Automatic Volume Limiter
Linear Mode
