Envelope follower in envelope filter.

POTL · November 18, 2018, 07:32:54 AM

Hi at the moment I am studying the work of envelope filters and I am interested in differences envelope follower, I look at the popular schemes Mu Tron and Mad Professor, they are similar, but the scheme Mad Professor looks more complicated.
I have 2 questions
1) is There any difference from the position of the diodes(which half-wave rectify), did it by ear or there is no difference?
2) Diagram the Mad Professor is much more difficult, which gives the second stage?

Rob Strand · November 18, 2018, 06:02:32 PM

QuoteHi at the moment I am studying the work of envelope filters and I am interested in differences envelope follower, I look at the popular schemes Mu Tron and Mad Professor, they are similar, but the scheme Mad Professor looks more complicated.
I have 2 questions
1) is There any difference from the position of the diodes(which half-wave rectify), did it by ear or there is no difference?
2) Diagram the Mad Professor is much more difficult, which gives the second stage?

Technically there are some significant differences.

The Mad Professor rectifier includes IC-C and IC-B. Without C4 present the output of IC-B would be an ideal full-wave rectified waveform. The addition of C4 provides filtering. The C4 and R9 time constant is about 40ms so it will filter most of the ripple yet capture the overall envelope. The most important difference about the filter is it is an averaging filter not a peak detecting filter. The output is the average of the full-wave rectified waveform. The characteristic of this filter is it has a slow to rise-up and go down. The up and down rates are equal. It does not catch the quickly catch the start of the peaks and decay down slowly like a peak detector. Following that is the normal peak detector. This peak detector uses a series diode with an opamp so it needs a minimum signal level before the envelope detector cuts in. The reason for using the averaging filter is to reduce the ripple and prevent the garble sound you sometimes get. The two stages provides two time constants. In the past I've found two time-constants to sound better.

The Mutron uses a peak detector. The diode is a precision diode (which uses an opamp) so it doesn't have the minimum voltage threshold you see on the Mad Professor. The "hidden" thing about the Mutron is it uses Vactrols. Vactrols have their own time constants; they are often asymmetrical like a peak detector. So while the *circuit* appears only to have the time constant at the peak detector, the overall behaviour is like it has two time constants.

Overall the significant difference is the ordering of the filters. One has filter before the peak detector and one after. Also, the Mutron will respond faster to the initial attack of the envelope.

Quote) is There any difference from the position of the diodes(which half-wave rectify), did it by ear or there is no difference?

It can make a minor difference to the sound. Look at the envelope shown in this thread. A guitar envelope is not symmetrical,

https://www.diystompboxes.com/smfforum/index.php?topic=121186.0

ElectricDruid · November 18, 2018, 07:18:51 PM

+1 what Rob said. (I seem to be following him around at the moment..)

The first example is a full-wave precision rectifier with additional smoothing. The second example is a half-wave precision rectifier followed by a peak detector.

They both do the same job (and probably pretty similarly), but they are quite different in several important respects.

The fact the diodes point "forwards" in one and "backwards" in the other is the least of those differences. That affects the polarity of the rectifier (whether you get the negative portion or the positive portion of the waveform) but that's all. If it's followed by an inverting stage of some type (like in the full-wave rectifier...oh!) then it amounts to the same thing.

Rob Strand · November 19, 2018, 01:19:30 AM

Quote+1 what Rob said. (I seem to be following him around at the moment..)

(The other phrase withheld

).

ElectricDruid · November 19, 2018, 02:59:10 PM

Quote from: Rob Strand on November 19, 2018, 01:19:30 AM
Quote+1 what Rob said. (I seem to be following him around at the moment..)

(The other phrase withheld ).

No,...

Rob Strand · November 19, 2018, 06:34:21 PM

QuoteNo,...

LOL. I'm blown away.

Tony Forestiere · November 19, 2018, 07:05:07 PM

Quote from: Rob Strand on November 19, 2018, 06:34:21 PM
LOL. I'm blown away.

Well played, Mr. Strand. Well played.

Tony Forestiere · November 19, 2018, 07:14:15 PM

Sorry. Double post.
The admiration still stands.

Rob Strand · November 19, 2018, 07:25:22 PM

QuoteWell played, Mr. Strand. Well played.

I can't help myself.

Rob Strand · November 20, 2018, 02:34:22 AM

POTL · November 21, 2018, 02:44:09 PM

Thanks, your answers helped me.
I consider it important to understand what you are collecting.
It now remains to find the optocouplers and compare
optocoupler vs photocell+LED vs OTA.

Technical GAS

amz-fx · November 22, 2018, 08:41:48 AM

Also consider that the Mu-Tron is working with a dual supply for the op amps while the MP only has a single 9v battery. This requires some circuit changes to function/bias properly.

regards, Jack

POTL · November 24, 2018, 11:33:38 AM

Hello
Yes, I took into account this moment.
In a YouTube video, the sound of Mu-Tron seems more natural and pleasant, perhaps these are differences in the scheme, perhaps the optics just sound nicer than OTA.
A little later, I want to collect both variants with the most identical parts of the circuit and understand exactly how much OTA and optics influence soundness.
In general, there are ideas for modernization, I was intrigued by the variation from 3Leaf Audio and I want to collect something similar.

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Envelope follower in envelope filter.