Hello, and a new project idea...

[rooster18]

Hello, I have been trying to get an account here, and was finally successful after a long time. I have an idea for a project, rather involved, and figured that this is a place that might enjoy such an adventure. This is one of those things that common doctrine says "can't be done", but rules are meant to be broken, so....

My keyboard player plays through a Leslie 147 cabinet. Amazing sound, and can't be duplicated. Wouldn't it be great, though, to have a pedal that could get us 90% of the way there? Now, as nice as the Univibe sounds, as well as the Phase 90, and other vibe/phase shifters, none of them really do the job, do they? So, I looked over this cabinet and realized a few basics that must be done to duplicate a Leslie. Here are the minimums:

First, you have to split the highs off from the lows, as the crossover in the cabinet does this into the spinning horn and the 15" woofer.

Second, they have to be phase-shifted at different rates, with the highs running at least twice the speed of the lows.

Third, there has to be a tremolo that runs in concert with the phase shifting; the volume has to oscillate between loudest and softest on each frequency section (the lows and highs) at 1/2 the speed of the phase shifter. This is because it's not just the phasing effect from the dopplar shift, it's also that the horn spins towards the back of the cabinet, as well as the baffle for the lows.

An adaptation with the LERA from R.G. Keen for the speeding up/slowing down of the motors.

I'm disregarding the overdrive characteristics of the poweramp for now, just the output from the speakers.

Whaddya think? I'd figure dual vibes along the lines of the neovibe/univibe with the tremolo locked in with the oscillator.

Don't know if I have time myself right now, but I'd like to try to do this in the fall. Meanwhile, if someone was looking to acheive the impossible, this one seems to me to be beyond the usual fuzz/boost/eq projects. It's a biggee, but what the heck. If I come up with a good one, I'll post the schematic.

rooster.

[alextheian-alex]

Give it a try.  I have seen a few early (tube) organ circuits that attempt that very thing, but i have never heard them in action.  A few guitar amp trems work in a similar way, but are not very convincing. 

[SeanCostello]

I think that the simulation circuit would need to be more compilcated than you describe, at least for the high rotor. The Leslie cabinet is a box, with speakers revolving around inside of it. The sound you hear is not just the direct sound from the speakers (which is time varying), but the very strong reflections from inside the box (which are also time varying, at a different phase than the direct sound). Plus, you have time-varying reflections from within the room. This is why the sound is perceived as a chorus, instead of as a vibrato - if it was just the direct sound from the rotor, it would be an amplitude-modulated vibrato.

A realistic model would use at least 4 time-varying sources for the horn - 1 for the direct sound, and 3 for the reflections. However, I bet you could get away with 2 sources, and get a pretty decent sound (I know that the Ensoniq Leslie model uses 2 chorus taps for the rotor).

The bass rotor may not need as complex of a circuit - perhaps simple amplitude modulation, or a swept 1-pole filter.

Sean Costello

[d95err]

The main factor in the spatious unpredictable sound of the Leslie is how the sound goes out in all directions, bouncing back from the walls at different angles. So, for a Leslie sim to be successful, it needs to be stereo.

[zjokka]

 You can build and tweak any electronic effect you want, but constructing a leslie is mostly about mechanics, not electronics. It will always be a 'simulation'

[blanik]

don't forget also the doppler effect, wich means a sound travaling from close to you to further away will also change pitch! so thats a third element... perhaps the hardest one to emulate properly...


R.

[zjokka]

also have a look at this thread:
http://www.diystompboxes.com/smfforum/index.php?topic=54018.0

[oldrocker]

I've had some Leslie type effect by connecting several pedals together.  Like a tremolo to simulate loudness of the speaker rotating.  A vibrato or slight chorus for the Doppler effect and phaser for frequency shift.  Adjust modulation speed on each device to accomplish somewhat of a Leslie sound.  As stated above if you could separate the highs and lows with separate speeds too.  I once used a the Tony Algood's cheap auto wah which sort of simulated the above statement.  It sounded good.  Of course it wasn't perfect by any means but it might fool the casual untrained listener.

[petemoore]

I've had some Leslie type effect by connecting several pedals together.
  Yupp...it's not the end 'leslie' emulation..where the fun is..
  Fun is in hooking it up and having fun with it.
  Different chainings and splits of output through...
  I use the echo park to get A/B outputs to two amps and wide placed speakers, then use phase before split, then tremolo, phase, reverb to one amp.
  It's amazing how phase shifted an amp with no phase shifter on it sounds when it's near an amp with phase shift on it.