Companding & Flanging

[redeffect]

i'm in the process of designing my own flanger. after scouring over as many schematics as i possibly get my hands on, i noticed one common thing. no companding. it seems that if there was ever an effect that was begging for companding, the flanger would be it. there seem to be 2 options. (1) pre input / post output: and (2) pre delay line/ post delay line (as per most analog delays). I want to institute true companding: not the common "Quasi/pre emphasis/post de-emphasis" thing that everyboby seems to do. I can easily buy one like that, so that would defeat the whole concept of "rolling my own". half the fun is building something that you cant find commercially(for me anyhow). any thoughts on this? ideas? real life experiences?
thanks .
red

[A.S.P.]

i love flanging...

[Mark Hammer]

Go to http://hammer.ampage.org and check out the documents for the PAiA Hyperflange, the issue of DEVICE that has the Flanger in it, and and the document called Anderflange.  There may be others, but these come to mind right now.

You are correct in that companding is not consistently used in the world of flangers, but it IS used.  Similarly, while you'd think that companding would be a natural for phase shifters, given the headroom limitations of FETs, the only commercial phaser I've seen that sticks acompander in there is the RPH-10 table-top phaser from Roland, and I think maybe the Moog Stage Phaser.  Other than that, unless there are obscure japanese, German or Danish products that don't show up on this continent, companding IS generally missing in action.  The Boss Dimension C chorus pedal uses companding, but there it is to avoid the risk/presence of clock heterodying from the dual BBDs/clocks on board.  Seems to me that Peavey made a companded chorus too. But companded flangers?  Not really.

So why don't you see companding in flangers?  A number of reasons:

• Headroom issues: you will often see a soft-distortion/clipping circuit in the input+regen mixing stage of commercial flangers.  This keeps the mixed signal from getting too out of hand for the BBD.  That's a big chunk of the battle right there - probably enough for companies to say "Well that takes care of that, and we didn't even have to figure how to cram more stuff into the box".   Even moreso, the soft-clipping adds a wee bit of harmonic content which can make the flanger sound richer.  So much for motivation to go beyond a 2-diode clipper!
• Hiss and whine issues: Flangers clock fastest of pretty much all the BBD-based effects, so reducing audible clock whine is generally less of an issue in flangers, relative to say analog delays, because the clock signal generally remains way out of hearing range.  In the realm of hiss, it seems to me that a great many companies do not aim for ultra-short delay times, so they don't need the audio bandwidth for those ultra-short delays to deliver audible notches.  Instead, they just pack a couple of poles of lowpass filtering on the delay path, and again, the problem is taken care of.

Could each of these issues be tended to more effectively by companding?  Sure.  But it ends up making for a bigger and more expensive pedal, for folks who may well not hear the difference.

[stm]

I used to have a Boss PH-2 phaser that had an NE570 in it.

[Mark Hammer]

Well I'll be!  I did not know they had those.    

[notchboy]

The Moog rack phaser also has a compander...

[stm]

I used to have a Boss PH-2 phaser that had an NE570 in it.

At the time I had it I was lazy to trace it, mainly because the huge amount of components (discretes) scared me... 
This phaser had a two pos switch (MODE I & II) to choose between LINEAR and EXPONENTIAL sweep. Both sounded different and interesting on their own.

My gift I would ask to Santa for this year would be a PH-2 schematic... 

[nelson]

The EHX Echoflanger I cloned has NE570 companding/expansion.

[notchboy]

The Mode switch on the PH-2 controls the number of stages of phasing.  IIRC, Mode I is 4 stages and Mode II is 12 stages.  I haven't played with mine in a while, but I don't remember the Mode setting having an effect on the sweep shape.

[Mark Hammer]

• PH-2:  I had always thought the modes were different numbers of stages too; it could have a sweep type as part of it but I'll refrain from offering up an opinion - my hit rate is not what it should be today!
• Moog: That was actually the one I was thinking of.  It's the 12-stage 3094-based one.
• Echoflanger: Of course it has a compander - there's echo in there.

Now, apparently one of the tricks of applying companding to flanging optimally is where you take your regen signal from and where it goes back to.  I honestly forget what those two points are, but you hav a choice of before or after, so argue it out amongst yourselves.

[StephenGiles]

I think the "grunge" that lurks within the flanged signal in uncompanded and minimally filtered flangers adds to the sound, for instance the EH Standard Electric Mistress and the ADA Flanger which are by far my favourite units. However, analogue flangers of a kind more likely to be used in a studio environment at line level probably benefit from companding. The 2 Craig Anderton studio flangers I built years ago, the AMS100 and the Hyperflanger (Mark you must finish yours!!) benefit from being quiet and not loosing too much of the gutsy flanging sound.
Stephen

[A.S.P.]

http://www.diystompboxes.com/smfforum/index.php?topic=40191.0

[notchboy]

Here's a vote for including more filtering and/or companding if you get to do a rackmount version of the Hoax....

[A.S.P.]

would a pre-/de-emphasizing or a "3rd way" be OK with you for a rack-/studio-/ or Tube- version?  ...

[notchboy]

A.S.P. -- I don't much care what technique is used as long as the results are good (quiet, low distortion, nice tone, doesn't mess up the high-regen behavior).

Now, I know that you're inclined to put at least one tube into anything that an audio signal flows through so I'm treading in dangerous territory by asking this... but in the case of a flanger, is there really anything to be gained by including a tube that you couldn't get from just using a tube preamp, DI, EQ, etc., outside the flanger?  What I mean is, it would be great to have a quiet, stereo-output, Hoax-on-steroids rack unit, but I'd prefer that the tube sound be optional.  Having said that, have you tried using a tube in the regen path?  Oooh, a clean / dirty-compressed regen switch that switched a tube in and out of the regen might be very cool.  But if you just want to have tubes in the input or output stages, I'd rather add that externally.  That's just me...

[A.S.P.]

there are people frequenting this forum,

[DiyFreaque]

ARP Quadra Phaser is another phaser that uses compansion.  Chorus/Flangewise - the ADA STD-1.  Interestingly, neither of these use the often-seen NE570/571;  (STD-1 uses NE572 and Quadra uses a fairly unique design made up of op amps and 4007's for the most part).

[redeffect]

thanks for all the great responses and feedback on this topic. i'll digest them all and work out something that'll work for me. this is why this forum totally rules. sharing of information is truly one of the finest things people can do. i wish you all a happy and peaceful holiday season. thanks to all again

red

ps: thanks A.S.P. , for the heads up on analog mikes book. i clicked on the link you setup, and ordered it within 2 minutes:)

[stm]

• PH-2:  I had always thought the modes were different numbers of stages too; it could have a sweep type as part of it but I'll refrain from offering up an opinion - my hit rate is not what it should be today!

The thing is as follows:

Boss PH-2 (Super Phaser) has a switch with modes I and II that change from linear to exponential sweep, with the same number of stages. To verify this we would need a schem 

Boss PH-3 (Phase Shifter) has a switch to set 4, 8, 10 and 12 stages, as well as two "barberpole" infinite Rise and Fall modes.

Now, apparently one of the tricks of applying companding to flanging optimally is where you take your regen signal from and where it goes back to.  I honestly forget what those two points are, but you hav a choice of before or after, so argue it out amongst yourselves.

The correct way to use a compander with a flanger is to "bracket" the BBD with the compand and expand stages, and do the regen path and addition to the input externally.  This is awful at first sight, since everytime the signal is recirculated it experiences the compansion process, thus suffering continuous degradation.  If you don't do it this way, then at the expander you will get the original companded signal added with the recirculated signals, and the expansion gain will be calculated incorrectly.  The companding and expanding processes are nonlinear; for instance, the ouput level after a compander is proportional to the square root of the average level of the input signal.

Take a look at Boss DM-2 (Delay) and Ibanez (AD-100?) delay pedals that have companding around the MN3005 and you will see what I mention.  Moreover, the flanging project in the Device Magazine was corrected the next issue because it had an error precisely with the regeneration signal.  Nevertheless, you will see that in the original issue the schematic has these corrections already hand drawn.

[notchboy]

Here are some excerpts from the PH-2 instruction booklet; I made no attempt to translate from Roland-ese:

The BOSS Phaser PH-2, featuring 12 stage phase shift circuits, allows stronger effect than any other phase shifting unit.  Two completely different phase effects are optional just by changing the position of the knob.  Adopting antilogarithm circuit in the filter, the PH-2 gives smooth modulation effect.

In the Mode I position, phase sound, deeply swelling from high frequency to low, is obtained.  The Mode II is a phase sound with sharp phase shifting effect.

The PH-2 page on bossarea.com quotes the 1987 Boss Pocket Dictionary as saying that Mode I is 10 stage and Mode II is 12 stage.