envelope follower IC chip

[pellikkan]

Hi All !
These days isn't there just an IC chip available that is an envelope follower?,
that is, a chip that will convert an AC audio frequency signal into a DC attack
and envelope curve ?? I'm looking for one that doesn't bleed off much of the
signal, or else you can run it off a signal after being preamped?? It seems one might
be available via ali baba or wherever?
Thanks in advance everyone!

[J M Fahey]

There might be a dedicated chip, why not? , but in any case you can design your own.
Basically a half or full wave active rectifier ( 1 or 2 Op Amps, 1 or 2 diodes inside the NFB loop) to extract the audio signal envelope and then you filter that with the time constants you want .
What do you want to control with it?

[nickb]

This has it and more THAT4301 THAT Corporation 4301 Analog Engine - Dynamics Processor IC

[pellikkan]

Hi there uall. Thanks so much for the excellent replies Nick and JM.

If you could direct me to a schematic of that op amp & diode follower that would be awesome.
I just want to control other chips with it is the deal, triggering on an attack curve and maybe triggering something at some cutoff level as well.

I'd have to investigate what it takes to trigger other chips as well, but I wanted to find an envelope follower for starters and go from there.
After all, isn't this still the age of object-oriented programming and modular engineering?

The 4301 chip appears quite versatile and affordable and promising. But I couldn't find an envelope follower configuration
among the many applications yet, but if you could point me to such a page that would be great.

Thanks so much for all your all's help!

[nickb]

The AC to DC bit is the "RMS" block in the THAT 4301. For compressors, using an RMS to DC rather than a peak detection is considered sonically preferable.

If you are going to use the DC signal to control gain then the chip also has a VCA and some spare opamps. It's a complete compressor in one chip. Page 4 of the datasheet gives you a complete schematic for a compressor. As shown the attack is very fast but t's easy enough to change.

I think it would help is we knew more about your application.

[Mark Hammer]

The 4301 is a great chip, but it generally requires as many external components as a from-scratch rectifier circuit does. There is not going to be any general-purpose one-size-fits-all envelope-follower chip, simply because the parameters will always be tailored to the specific application. heck, even or an autowah aimed at bass rather than guitar, you need to change component values.

However, feel free to browse their datahseets - THAT IC Datasheets - and their suggested design applications - Design Notes for THAT ICs - to see if their products cater to your needs.

[pellikkan]

Yes, I see your point about say guitar vs bass autowah. Surely it's somewhat of the same
problems in sound wave frequencies as EM frequencies, i.e., the huge horn used
by penzias and wilson to detect microwaves from outer space would be useless
to detect xray or gamma sources, etc. Hell, even phonon detection surely gets quite
frequency dependent I'm sure.

I can see where an envelope follower chip
might only cover a certain band of frequencies,
one for bass being useless for one for guitar, etc.
I can see your point that one must probably make a
tuned RLC or RLC+op amp circuit for different applications.

I guess in that case the burden of circuit parameters and maybe
even circuit configuration is upon me.

Let's say that I'd like to make a
bass autowah like you mention. If that were the case could you point
me to a schematic somewhere?

I don't have any specific application in mind, ..just wanna make pedals
that do different stuff, and I thought an envelope follower would be a good place to start.
I'm not playing out so much anymore, but still want to make contributions somehow.

Speaking digitally as opposed to analog though, it seems possible that frequency dependence
would be much less important. That is, as soon as the signal was converted to numbers,
all that would be left would be math, logic, sample speed, and latency, instead of component dependence.
I'm not an expert but maybe there is a digital based envelope follower that has much less
frequency dependence??

[cjlectronics]

If they only had a Quad matched JFET IC... Matching JFETs for phasers is a pain in the butt (and I'm getting lazy in my old age)

[pellikkan]

even or an autowah aimed at bass rather than guitar, you need to change component values..

Thanks much for great replies.
I don't want to impose on others to do my web searching, but if you know
of a circuit somewhere that would function as an envelope follower for
the bass autowah you mention, then maybe you could point me to it?
Or the whole bass autowah circuit would be ok as well, (especially if
it is not too hard identifying the envelope follower part of it.)

[Mark Hammer]

Almost any auto-wah circuit is easily adapted/optimized for bass by implementing the following changes/mods:
1) The sweep range should be bumped down by an octave or so. So if the filter normally uses a pair of .01uf caps to set the filter range, change them for .022uf to shift it downwards.
2) Bass is often as much a percuission instrument as it is anything else. As such, it needs to help emphasizing the beat. A faster decay often sounds better when autowahing a bass, compared to a slowly resettling filter sweep. That faster decay can be achieved by sticking a (fixed or variable) resistance in parallel with the averaging capacitor going to ground. That resistance discharges the cap faster than it would on its own, bringing the filter back to its starting point quickly.
3) Mixing in some clean signal with the filtered. Optimally, one uses a lowpass filter for bass, since it retains the fundamental and "thump" all the time and simply varies the harmonic content. That said, in the world of analog filters, it is often easier to design, and cheaper to build, a swept bandpass filter. Even if you shift the sweep range lower via #1, and make it return to bottom faster, via #2, sweeping a bandpoass upwards, even if only for a split-second, robs the signal of the bottom. So the solution is to mix in at least a bit of clean signal, so that the foundation remains as the hamonic content is varied by the filter.

[pellikkan]

sounds like a good plan, I guess now I'll have to find such an autowah circuit and parse it for
the different components, i.e., the envelope follower part, the voltage controlled band pass,
maybe a mixer in there too?, etc. Again,..only if you know already where to point me to
a good circuit then please lemme know, thx. I'll look around.

[Steve A.]

This doesn't answer your original question but the Craig Anderton books on guitar effects included an envelope follower module which I added to many of his projects, usually with great results. (I built most of his projects back in the 80's including an 8 channel mixer which was kinda noisy because of the RC4739 chips used- I was glad to replace that with Yamaha mixer in my home studio after getting my tax refund the following year.)

Steve Ahola

[Mark Hammer]

Topopiccione Electronics Inc. - Electro-Harmonix BassBalls