[sdiy] Harry Bissell's guitar synth envelope follower

[Tom Wiltshire]

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