Author Topic: Lack of aliasing filter in the Electric mistress, as well as limiting diodes  (Read 630 times)

maxdm

Hello all,

I am looking at the differences in design between different flangers, and I have noticed that the signal path for the Electric Mistress is quite different, in the sense that there is no low pass filtering on the input of the delay chip.    There also aren't any back to back diodes in the feedback loop.  The only filtering I see is something akin to RIAA eq, for records,  with a bass cut and bass boost, apparently to get a few dB higher modulation level.

Now, last time I played with an original was decades ago, so I do not know the sound of the circuit well enough.

My question is:  How does the lack of aliasing affect the way the flanger sounds, and how does the lack of limiting diodes affect the sound quality of the resonance, when pushed to near-oscillation?

ElectricDruid

As long as you don't feed it any signals that go above Nyquist, the lack of anti-alising filtering shouldn't make any difference. The main effect of the lack of that filtering is to make the pedal less "robust" in the sense that it'll only work with certain signals with a limited bandwidth. If you start feeding it a signal with a lot of high frequency hash, it's going to start aliasing like hell and will probably sound awful as alising sidebands sweep down as the flanger sweeps up and so on. Maybe you can call that "character". Maybe. In my view, it's simply a cost-saving measure by ElectroHarmonix, not any kind of sensible design decision. It's "cost engineering" - what else can we take out before this breaks?

Vivek

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A distortion would create a lot of higher order harmonics

It's possible that the one with filters accepts a distortion pedal in front in a more graceful matter than the circuit without the filters.
« Last Edit: August 03, 2022, 02:48:41 PM by Vivek »

Rob Strand

Quote
In my view, it's simply a cost-saving measure by ElectroHarmonix, not any kind of sensible design decision.
+1 from me too.   Could turn out that in the end overloading the BBD sounds worse than not having the diodes, despite the lack of filtering.
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ElectricDruid

Could turn out that in the end overloading the BBD sounds worse than not having the diodes, despite the lack of filtering.
That was exactly why I put limiting diodes on the input mixer in my Flangelicious design. Overdriving the BBD sounded terrible, whereas deliberately soft-limiting the signal ahead of the BBD to a level the BBD could cope with just adds some warmth and harmonics that a flanger can really work with.

StephenGiles

Arguably one of the best sounding flangers ever designed!!
"I want my meat burned, like St Joan. Bring me pickles and vicious mustards to pierce the tongue like Cardigan's Lancers.".

ElectricDruid

Arguably one of the best sounding flangers ever designed!!
It certainly has that reputation. Perhaps that is because it's one of the *least limited* flangers, in the technical sense of bandwidth.

I'm not sure. I've never had an original to play with and pull to bits and if I did nowadays, I doubt I'd want to mess with it that much.

StephenGiles

I built an EM using a TDA1022 and included the bounce circuit from the Eventide Instant Flanger - great fun!!

I did draw out the circuit but can't find it at the moment.
« Last Edit: August 06, 2022, 07:17:41 AM by StephenGiles »
"I want my meat burned, like St Joan. Bring me pickles and vicious mustards to pierce the tongue like Cardigan's Lancers.".