Toggle navigation

Gallery

Register

Login

1 Hour
1 Day 1
Week 1 Month
Forever

GroupDIY

Project Specific Discussions

Dynamic
Processors

PWM Compression...

News:

Smart Search:  If you're...
-not in a board, it will search the
entire forum.
-in a board, it will search just that board.
-viewing a
topic, it searches within that topic.

7 Likes

«
previous

next
»

Print

Pages: [1]

taliska

Member
London, UK.

Posts:
114

PWM Compression...

« on: August 21, 2014, 04:27:23 AM
»

Hi all,

I don't know whether it's been
posted before, but I stumbled across a DIY PWM compressor that I hadn't seen
before.

It's from an italian guy who makes plug-ins and some hardware
units too. The PWM project seems to have been run in collaboration with a music
mag of some sort and the page for it is here:

http://www.sknote.it/MS4_en.htm

I found it because I
randomly googled for a sta-level plugin (which this guy also makes) after
finding a sta-level schematic online, but with too many unfinished builds as it
is, I figured I'd go the plug-in route on the sta. (Won't be building this pwm
either as I'm already working up to building the AC Sound pye, but it might be
interesting for someone to have a look at for curiosity's
sake...).

Cheers,

Kaz

P.S. The sta-level schematic was this
one if it's any use to anyone: http://www.audioschematics.dk/downloads/schematics/amplifiers/sta_level.jpg

Logged

gyraf

Global Moderator

Member
Aarhus, Denmark

Posts:
7387

Re: PWM Compression...

« Reply #1 on: August 22, 2014, 07:58:40
AM »

Unfortunately no schematic or other
info...

Jakob E.

Logged

..note to self: don't let
Harman run your company..

taliska

Member
London, UK.

Posts:
114

Re: PWM Compression...

« Reply #2 on: August 22, 2014, 09:07:42
AM »

Quote
from: gyraf on August 22, 2014, 07:58:40 AM

Unfortunately no schematic or other
info...

Jakob E.

Yeah, I didn't look further in to it
myself and unfortunately I don't speak or read Italian.

For those that
do, look at:

http://www.compmusic.it/costruisci-il-compressore-ms4-stereo-in-pwm-primi-passi/

(looks
like there might be a link to an online copy of the magazine at the right hand
side...perhaps that will contain more info?)

And the almost non-existent
discussion of the project at:

http://mixincafe.com/index.php/Thread/5776-Compressore-MS4-con-Computer-Music-Studio-Thread-di-supporto-in-italiano/?postID=70088#post70088

As
a last resort, could always try e-mailing the guy himself at [email-masked].

Of course, who knows
whether the juice will be worth the squeeze, but it seems like it might be of
interest to those who want both feedback and
feedforward...

<edit>
Just googled to try and locate a
schematic, but no info, so perhaps this is more of a closed project. Came across
a thread on GS of people discussing his plug-ins, and there is a brief mention
of the MS4 which suggests it's actually very new...(looks like it was released
around May/June...)

Actually...just found the support thread on kvr: (no
entries yet, but English at least...)

http://www.kvraudio.com/forum/viewtopic.php?f=49&t=412438&sid=0db833080421d2214b9aca60165d38f9

</edit>

Cheers,

Kaz

« Last Edit: August 22,
2014, 09:43:15 AM by taliska »

Logged

Mictester

Member

Posts:
1

Re: PWM Compression...

« Reply #3 on: September 18, 2014,
06:58:36 PM »

I did a lot of work on PWM compressor /
limiters for broadcast use.
PWM as a means of control is very elegant.  As long as the switching
frequency is well above the audio range, and you include lowpass filters to
eliminate any possibility of aliasing or control breakthrough to the output, the
results can be superb.  You aren't at all concerned about the linearity of
the control elements and you don't need to match them for stereo use - they are
either on or off!  My designs (mostly) used the 4066 CMOS switch IC as the
control element.  Each IC has four switches, and these are very accurately
matched (within the same IC).

The sidechain was done in the usual way,
with buffer amplifiers from the input combined to mono, then feeding a full-wave
rectifier and timing circuit using a diode pump.  The derived DC
voltage was then used to control the pulse duration of an oscillator. Again, I
used a CMOS IC for this function.

The audio path for each channel used a
"Superbal" input stage (a nifty way of getting superb CMRR) using an NE5532,
driving another NE5532 stage for pre-emphasis, then feeding a pair of Sallen and
Key low pass filter stages which turned over at 15 kHz (this was for broadcast,
remember).  The Control oscillator ran at 120kHz (well outside the
broadcast bandwidth), and the pulse width varied from 3% to 90% (roughly).
The CMOS switches were wired with one in series with the audio and then a second
switch to ground.  The switches in each channel were switched with a pair
of complementary square waves from the PWM oscillator.   The series
switch was "on" when the one to ground was "off", allowing audio through, and
vice versa......

The switching stage was followed by a further pair of
15kHz lowpass filters, and then on into a current-pump balanced output
stage.

I found that it was necessary to shape the frequency response of
the sidechain input amplifiers for best results, and I built a series of these
units with BBD "analogue" delay lines before the gain control stages, so that
the "attack" phase was eliminated, thereby giving a broadcast limiter that
didn't overshoot and didn't require a nasty clipper after it to catch the
peaks!  I built about 200 of these devices, and many of them are still in
use today, over 25 years later!

Logged

dogma,
Dr Gris, Script, PRR,
shot and

2 others like this

desun

Member
London, England

Posts:
34

Re: PWM Compression...

« Reply #4 on: October 02, 2014,
10:38:29 AM »

Quote
from: Mictester on September 18, 2014, 06:58:36 PM

I did a lot of work on PWM compressor /
limiters for broadcast use.  PWM as a means of control
is very elegant.  As long as the switching frequency is well above the
audio range, and you include lowpass filters to eliminate any possibility of
aliasing or control breakthrough to the output, the results can be
superb.  You aren't at all concerned about the linearity of the control
elements and you don't need to match them for stereo use - they are either on
or off!  My designs (mostly) used the 4066 CMOS switch IC as the control
element.  Each IC has four switches, and these are very accurately
matched (within the same IC).

The sidechain was done in the usual way,
with buffer amplifiers from the input combined to mono, then feeding a
full-wave rectifier and timing circuit using a diode pump.
The derived DC voltage was then used to control the pulse duration of an
oscillator. Again, I used a CMOS IC for this function.

The audio path
for each channel used a "Superbal" input stage (a nifty way of getting superb
CMRR) using an NE5532, driving another NE5532 stage for pre-emphasis, then
feeding a pair of Sallen and Key low pass filter stages which turned over at
15 kHz (this was for broadcast, remember).  The Control oscillator ran at
120kHz (well outside the broadcast bandwidth), and the pulse width varied from
3% to 90% (roughly).  The CMOS switches were wired with one in series
with the audio and then a second switch to ground.  The switches in each
channel were switched with a pair of complementary square waves from the PWM
oscillator.   The series switch was "on" when the one to ground was
"off", allowing audio through, and vice versa......

The switching stage
was followed by a further pair of 15kHz lowpass filters, and then on into a
current-pump balanced output stage.

I found that it was necessary to
shape the frequency response of the sidechain input amplifiers for best
results, and I built a series of these units with BBD "analogue" delay lines
before the gain control stages, so that the "attack" phase was eliminated,
thereby giving a broadcast limiter that didn't overshoot and didn't require a
nasty clipper after it to catch the peaks!  I built about 200 of these
devices, and many of them are still in use today, over 25 years
later!

This is some great info, thanks for
registering and telling us about them!

Logged

ruairioflaherty

Member
Los Angeles

Posts:
1538

Re: PWM Compression...

« Reply #5 on: November 12, 2014,
11:57:08 PM »

Yes, thanks Mictester, fascinating
stuff.

Can you/would you share a schematic?  I understand that it
might be IP you need to protect.  I'd be interested in seeing how it all
goes together.

Logged

Print

Pages: [1]

«
previous

next
»

GroupDIY

Project Specific Discussions

Dynamic
Processors

PWM Compression...

Related Topics

Subject / Started by

Replies

Last
post

parallel
compression: can someone please add to this ...

Started by ToobieSnack
« 1
2 »
The
Lab

28 Replies

2789 Views

September 21, 2005, 04:21:20 AM
by clintrubber

DBX
119 - No Compression

Started by Jim50hertz
The
Lab

1 Replies

627 Views

March 31, 2006, 01:44:23 PM
by Jim50hertz

DBX117
More compression please! DBX 117

Started by OldMan
The
Lab

5 Replies

2011 Views

October 08, 2006, 04:18:16 PM
by SSLtech

Too
much compression

Started by kag2020
The
Lab

2 Replies

944 Views

July 02, 2007, 04:21:58 AM
by gyraf

Help
with LA-2A no compression

Started by jwhmca
The
Lab

16 Replies

622 Views

March 24, 2013, 11:24:13 PM
by CJ

Policies

SMF 2.0.6 | SMF © 2013, Simple Machines