electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Articles  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links  |  Store
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
Live streaming at radio.electro-music.com

  host / artist show at your time
  Jez Adventures in Sound
Please visit the chat
 Forum index » DIY Hardware and Software
Slew filter
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 1 [2 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
prgdeltablues



Joined: Sep 25, 2006
Posts: 162
Location: UK
Audio files: 10

PostPosted: Sun Sep 29, 2013 11:47 am    Post subject: Slew filter Reply with quote  Mark this post and the followings unread

I've just finished up a new circuit which I thought I'd share. It's a slew filter - a slew rate limiter working in the audio range. I couldn't find an example on the internet, though would expect it's been done before. This one is based on an article that was apparently published in Electronic Engineering in 1995, but adapted for audio frequencies and with some other changes.

The effect of the module is that when a sine wave signal is input, above a certain frequency, it is gradually changed to a triangle wave, and then, as the frequency is increased higher, the amplitude reduces. This circuit also has separate control of the up and down slew rates, meaning the output can range from a saw through a triangle to a ramp waveform. The cut-off frequency can be voltage controlled, though not with as wide a range as the panel pot.

The overall effect is fairly subtle, more a change in timbre than an aggressive filter. It's quite neat for adding a bit of oomph to the bass end.

Sound clips to follow.

There's some DC offset in the signal, especially as the cut-off frequency is being changed, so I've decoupled the output. As I had panel space, I've added a switch to bring in a higher value slewing capacitor, which pushed the range down into LFO frequencies, and this signal is DC coupled.

The circuit works in two ways. The frequency pot P5 acts with the caps (C1 and C2) to form the usual RC filter found in most slew limiters. But the maximum permitted slew rate is also controlled by the two circuits around U2 and U3, which act to constrain the voltage across R2/P5 to a constant and thus causing a constant current to flow into C1/2 meaning the voltage across the capacitor rises linearly at a set maximum rate. When the rate of voltage change of the input signal is less than the maximum so constrained, the filter has no effect and the waveform of the signal is passed unchanged. But as the frequency of the input signal rises, the rate of voltage change (particularly in the middle part of a sine wave), exceeds this max, and the output signal is clamped to a linear rate of voltage change ie a triangular waveform.

The change from sine to triangle happens over about two octaves.

Peter


slew filter.png
 Description:
 Filesize:  24.04 KB
 Viewed:  62 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

slew filter.png


Back to top
View user's profile Send private message
prgdeltablues



Joined: Sep 25, 2006
Posts: 162
Location: UK
Audio files: 10

PostPosted: Sun Sep 29, 2013 12:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

A couple of sound samples of the slewfilter. #3 is a simple scale, at first played just with a saw wave, then with a sine wave run through the slewfilter added in, you can hear the sine emphasizing the bass end, then morphing into a doubled triangle wave at higher frequencies

#2 is a noodle, applying an LFO to the CV input, which causes both a change in timbre and volume, then from about 1.20 onwards, playing with the up and down slew knobs too, to morph from saw to ramp.


slewfilter#3.mp3
 Description:

Download
 Filename:  slewfilter#3.mp3
 Filesize:  1.57 MB
 Downloaded:  63 Time(s)


slewfilter#2.mp3
 Description:

Download
 Filename:  slewfilter#2.mp3
 Filesize:  6.46 MB
 Downloaded:  63 Time(s)

Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 1 [2 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
AmbiphonicDSP

Please support our site. If you click through and buy from
our affiliate partners, we earn a small commission.


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use