Tape delay sim?

[Arno van der Heijden]

Anybody ever thought about doing a tape delay sim? There are some commercial products on the market that can do this (Line 6, H&K Replex) but I figured this might be a cool project or give people some ideas.

I was thinking about a tape delay sim based on a digital delay chip, much like Scott Swartz's PT-80.
What if we took the signal path of an Echoplex, the tube version for example, replace the tubes with fets and use a PT2399 to provide delay.
Add some tape compression:
http://home3.netcarrier.com/~lxh2/tapesat.html
You could even use an LED/LDR combo to modulate the delay time and introduce some wow and flutter effects (or just cool modulated delay sounds).

Would this be feasible? No?
Note that I have never actually played a tape delay myself, but they seem to be the holy grail of delay sounds. Also I'm sure I'm overlooking some other things that are characteristic to the sound. The frequency response of the record and playback heads might need to be taken into account as well.
Opinions? Ideas? Additions?

[Nasse]

Been thinkin that too. Maybe modular system would be nice. Voltage or logig level controlled for presets. Multi-head tape echo simulator.

Most of old but favourable machines had just three, four or five heads. Lots of info available. I think PT 2399 delay time range is just ideal. The "rautalanka" quys just tune tape heads "wrong" so it sounds better.

[EdJ]

That sounds like a very cool project indeed!
I have owned tape delays in the past but never bothered to take them with me in those crappy old vans.A solid state version could take care of that part of playing too :wink:
Ed

[Mark Hammer]

Some sort of diode-based soft-compression is probably appropriate in the mixing output stage to mimic the headroom limitations of tape.  So, for instance, an op-amp with a set of back to back Ge diodes with a variable resistor in series (in addition to a feedback resistor) to adjust the compression/clipping curve.  

Note that this is often used with BBD's in the input mixing stage (where the recirculated and input signal are mixed to gether) to keep the regeneration+input from exceeding the headroom of the BBD.  No reason why you couldn't insert it downstream to provide both coloration and soft compression.  I wouldn't be a bit surprised if this is what some of the digital-based delay lines that proclaim "analog tone" use to achieve it.

[Arno van der Heijden]

Some sort of diode-based soft-compression is probably appropriate in the mixing output stage to mimic the headroom limitations of tape.

Mark, do you mean something like this:
http://home3.netcarrier.com/~lxh2/tapesat2.gif

[Mark Hammer]

Yup.

[Steben]

Uhm... Isn't this just a filtered clipper?......

Maybe 1N34 in the non-inverting feedback loop is better and softer.
Combined with some high-roll-off this would be nice with some digital delay added.

[Maneco]

I think this would be a great addition to a project like the rebote delay 2 from tonepad...the delay line should be inserted between the opamp buffer and the 22k  resistor;this would also have the side effect of noise reduction,because there's preemphasis in the first  opamp stage,and de emphasis in the output filter...the wow and flutter can be simulated by paralleling an ldr with the time delay pot;an lfo should drive a led that illuminates the ldr...
Believe me,the ldr trick works... :wink:

[gez]

I was wondering if something could be done with Voice Record/Playback chips?  Haven't read any data sheets so I don't know if they could be looped though (might be able to do this with a PIC).  That aside, they're not cheap and re-record on the the ones I've seen is 'typically 100 000 times'.  Wouldn't last long if 1 second loops are your thing...but you can record loops lasting minutes!  :twisted:

[puretube]

they got a nasty habit (in fact 2):

1.:automatic power down;
2.:they wanna record a whole column,
instead of stopping where you want,
and then (you want it to) repeat immediately.

[Maneco]

the zvex llofi loop junkie is based in the 20 seconds voice rec/play chip...
here's a diy  version...

http://humano.ya.com/guruzeta/Guitarra/dirtysam/

the vibrato can be added by modulating the positive supply to the play/rec chip...

happy sampling....

[runmikeyrun]

what about a small two track reel to reel with delay?  Loop the tape around the reels and there ya go.  On the flipside, it's large, heavy, and you only have as many delay speeds as you have tape speeds.  But it is tape.

[runmikeyrun]

Arno,

are there any known sound samples of the tape saturation sim?

Thanks,
Mike

[runmikeyrun]

Arno,

are there any known sound samples of the tape saturation sim?

Thanks,
Mike

[Arno van der Heijden]

Not that I'm aware of.

[Arno van der Heijden]

This is the idea I have:
http://members.home.nl/a.c.vanderheijden/echosimplex.JPG

Some tube-like dirt could be added by using fets for the gain stages, much like ROG's amp sims.

[Mark Hammer]

Even if there were samples posted around, there is tape and there is tape.  Tape run clean is different than tape with the meters pegged, and 1.5 mil chrome tape is not the same as 0.5mil ferrous tape, just as tape with companding ain't the same as tape without companding.  

What you want is something that is adjustable to yield what it is about "tape-based delay" that you like, or seek at that time.  I think that an asymmetrical GE diode arrangement in an op-amp feedback loop with a variable series resistor and a few switchable feedback-cap choices might be just the ticket for some folks.

Note that older tube-based Echoplexes have two things going for them: tape AND tubes.  If your intent is to mimic an Echoplex, then you might want something that aims to mimic what the *tape* does, in addition to something that mimics what the "tubes* do.  That has implications for where the saturation emulator goes.  If you just want to mimic tape then it needs to apply to the delay path only.  If you want to mimic tubes and tape, then it needs to apply to the entire signal, in which case you may need one saturation emulator for the delay path and another for the mixer/output stage.

[Arno van der Heijden]

Mark,

Like I said before, I never played a tape-based delay so there isn't one specific thing I'm looking for as far as sound goes.

My idea was to simulate a *tube* echoplex and use fets to mimic tubes.  The echoplex' signal path can easiliy be recreated with fets. This might give a nice coloration to the signal or even a *touch* of overdriven tube sound (care must be taken not to overdrive the delay line).

Can you explain why the saturation simulator needs to apply to the entire signal or a second one for the output stage? I'm not sure I understand....

[Mark Hammer]

If you're layering signal on top of signal, there comes a point where the tape itself can't really handle more stuff than what you've got on it already.  Remember, where digital delay  simply recodes what's already there and what's mixed back in to a new digital signal, analog tape has to cram more signal on.

So, there is the effect of running an input signal through tubes and tape "hot" in general (mimicked by applying a saturation simulator to the entire output signal), and the effect of saturating the tape through use of regeneration that exceeds the amount of signal the tape can hold.  That's why I suggest the two separate circuits.  Pure speculation on my part, though.

[Nasse]

I would add some tube simulation to the direct path too, and try that compress thing in front of that delay line.