Yes, that's right-the first stage is usually a full-wave rectifier. This
makes the "negative" phase of the input signal "positive" and "fills in the
holes" between phases of the positive portions of the input signal. Picture
a repeating triangle wave, and then "fold up" the bottom portion along the
zero crossing line (in the case of a triangle giving you a triangle at
double the frequency, but that's not important here-we're extracting
amplitude, not frequency).
If one were to put in a theoretically perfect pulse wave, the FW
rectification would turn that into DC. ∗Theoretically∗, but nothing in
nature/analog ever works that way. But I mention it because sometimes an EF
will have a clipping circuit on the input before the rectifier in order to
"square up" the signal, and reduce the filtering required (as outlined in
the next paragraph).
In any case, the result then goes to an integrator to filter out the ripple.
Since the input signal can be anywhere from 0-20kHz in frequency, usually
there is a "Range" control, such a as three position switch, to control the
general "speed" of the integrator, tailoring it to a good range for the
input signal. That gives you a voltage out corresponding pretty nicely with
the envelope of the input signal, which is the _general_ amplitude at any
particular time (not following every peak-and-trough of the waveform).
Finally, some of this is tapped off and fed to something like a Schmidtt
(sp?) Trigger to produce a gate. (It's cool, by the way, when you can set
the rise/fall thresholds here, because you can create a flexible gate
delay/hold that way.)
So anyway, lag is similar to the 'smoothing' portion of a classic Envelope
Follower, but in itself doesn't really do the same job.
-----Original Message-----
From:
jwbarlow@... [mailto:
jwbarlow@...]
Sent:Thursday, 20 July, 2000 9:47 AM
To:
motm@egroups.comSubject:Re: [motm] Re: lag as EF
In a message dated 7/19/2000 11:31:13 PM,
elhardt@... writes:
>> Well I could be wrong, but once the Lag Processor is available, won't
>you
>> have the makings of an envelope follower?
>
>perpetual@... writes:
>>>enh? do enlighten...<<
>
>I thought somebody else would chime in before I got back to this. I would
>assume if you run a guitar or mic or any other audio source into the lag
>processor, then connect the lag processors output to whatever CV
destination
>you want to control, that is basically an envelope follower.
When I have run my preamped guitar through a lag processor the output is
filtered with like a simple 1 pole LPF.
I believe an envelope follower has (at least) full wave rectification since
an AC wave has no DC component. The rectifier, I think, would introduce a DC
component which was directly proportional to the amplitude of the input
signal. Clearly some filtering is needed to smooth out the "HF" stuff, but I
think that would be post rectifier -- note: I haven't looked at a schematic
of an EF in a long time, but I know that a LP will merely filter the audio
like a grainy tone control.