[sdiy] Harry Bissell's guitar synth envelope follower

[BrightBoy]

Here's a burning question I've had lately....

What happened to Harry?

He used to be quite active on this list and Analogue Heaven
and then suddenly disappeared.

Has he moved his participation to a different forum(s)?

Jeff

-----Original Message-----

>From: Tom Wiltshire <tom at electricdruid.net>
>Sent: Nov 25, 2015 5:57 PM
>To: synthdiy diy <synth-diy at dropmix.xs4all.nl>
>Subject: [sdiy] Harry Bissell's guitar synth envelope follower
>
>Hi All,
>
>I've been studying Harry Bissell's clever envelope follower, as described in full here, if you haven't seen it:
>
>	http://m.eet.com/media/1141271/18042-122602di.pdf
>
>I've got a question about the output filtering. The relevant section is here:
>
>	http://electricdruid.net/images/HarryBisselEnvFollow.png
>
>I understand the round-robin resetting of the three peak detectors. That bit is ok. Please give me a hand getting my head around the next bit;
>
>The three diodes provide the highest of the peak detector outputs (minus the diode drop, presumably) to the filter network.
>The filter network consists of D28+R208, R205, C67, and R321 (note that this is 10K here, but 1K in the article).
>
>Now, what I don't get is what the time constants of the filter are. Would it be the following? -
>
>1) R205 + C67 provide the attack constant, except…
>2) When D28 conducts (e.g. large rapid attacks) R208 will dominate the attack constant ( R208 and R205 in parallel)
>3) R321 + C67 provide the decay constant.
>
>Have I got this right?
>
>Thanks!
>Tom
>
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