Re: Stereo EDP

[Kim Flint <kflint@loopers-delight.com>]

At 07:14 AM 8/15/2001, Dennis Leas wrote:
>Hummmm....Gerry's message regarding his stereo EDP operational problems 
>make
>me think about how stereo operation works for the EDP...
>
>Using the EFC-7 footswitch (or equivalent) or front panel switch, you tap
>RECORD on the master EDP.  The master sends a MIDI note-on/off to the 
>slave
>to start recording.  Likewise, to stop recording, you tap RECORD on the
>master EDP and it sends a MIDI note-on/off to the slave to stop the
>recording.

that is mostly right, but you are forgetting about the brothersync 
connection that is necessary for putting multiple echoplexes together like 
this. It does two things, one is to synchronize the actual system clocks 
of 
the different units to operate at the same frequency. That keeps them from 
drifting over time.  The second thing is to provide a precise indication 
of 
when the Record button is pressed. That combined with midi is how the 
stereo operation works.


>Since MIDI commands take about 1 millisecond (a little less actually) to
>transmit, doesn't this mean that there is a phase difference between the
>left and right channel?  I.e., the slave signal will be shifted in phase
>with respect to the right.

if you relied entirely on midi, you would have these problems. Worse, it 
would drift around as the loops played, making it obvious. If the two 
channels are slightly out of phase you probably wouldn't notice it if it 
stayed constant. That is something the brothersync helps ensure on a 
stereo 
echoplex setup. It keeps them locked together at the sample level.


>Even with *real* clever programming, this characteristic would be hard to
>compensate for.


Matthias has been quite clever in sorting this whole problem out. It 
really 
does work!


>On the other hand, if you used a MIDI footswitch to trigger the EDPs, both
>master and slave would recieve the RECORD commands simultaneously 
>resulting
>in no phase error.
>
>Conclusion: For "perfect" stereo looping with the EDP, use a MIDI
>footswitch.

I think it could come out worse actually, since you are dependent on where 
each unit is in it's internal software polling for midi events. And you 
wouldn't have Matthias' clever programming to help you. In practice 
though, 
I don't think I noticed any issues either way. The basic setup of having 
the master unit send commands to the slave, along with the brothersync 
connections, works very well.

kim



______________________________________________________________________
Kim Flint                     | Looper's Delight
kflint@loopers-delight.com    | http://www.loopers-delight.com