Dual Echo Pros for Stereo Looping, First Impressions...

[Mech <mech@m3ch.net>]

Given the recent blowout by Line 6 of their rack mount modelers, I took 
the 
plunge and grabbed a second Line 6 Echo Pro, figuring that if I didn't get 
this harebrained scheme to work I could probably turn it around on Ebay 
for 
what I paid.  Since a few people on the list were at least curious about 
the viability of doing this, here's a quick write-up of what I've seen 
thusfar.


"What The Hell Are You Doing And Why???"

Okay, some background: My current looping setup already consists of two 
loopers, working asynchronously (hi mark!).  The main looper is my 
Repeater, which is connected into the effects loop on my mixer.  However, 
I'd also hardwired my Echo Pro into my E-mu Morpheus so I could use it for 
looped textures, drones, and effects.  Like many other E-mu units, you can 
actually use the multiple outs on the back of the Morpheus as effect 
send/returns to integrate external effects directly into the synth 
architecture.  Thus, the Echo Pro was directly wired into the Morpheus.

As we already know, the Loop Sampler algorithm on the Echo Pro is 
mono.  And, while working with the Morpheus, I started to become quite 
aggravated at the fact that I was able to come up with these cool, swirly, 
stereo textures that were then squashed down into a fair approximation of 
an AM radio as soon as I looped them.

Thus, I came up with the idea that I'd try running *two* Echo Pros -- both 
in mono -- respectively across each side of the stereo spread.  The units 
would each be set to the same MIDI channel to ensure that they could be 
triggered and controlled simultaneously.  At least at the outset, the 
patches would likewise be identical on both units.

So, in short the dual Echo Pros would be simulating a single stereo looper.


"Um, That Won't Really Work, Now Will It?"

For anyone else planning on doing something similar, there's one important 
caveat to this scheme that has to be stated up front.  There is no 
available mechanism to provide continuous synchronization between the two 
Echo Pros.  We're merely starting and looping the two units at the exact 
same millisecond via MIDI.  Unfortunately, the looper in the Echo Pro will 
not sync to MIDI clock, and there certainly isn't anything approaching the 
sample-accurate Brother Sync on the EDP (however, the overall solution 
using Echo Pros also costs a quarter of what one would have to pay for a 
pair of synced EDP's).

As Kim himself has mentioned on the LD list earlier, there is no such 
thing 
as a pair of perfectly identical clock sources.  If you took two identical 
stopwatches and started them at exactly the same instant, they would still 
eventually drift apart without any sort of external mechanism to 
continually bring them back into sync.

That is just what we're talking about here, so it's understood that the 
loops *will* eventually drift out of sync between the left and right 
channels.  The main point of the experiment is to see just how badly 
they'll drift, or if the drift can be used in an interesting manner.


"You've Bored Us To Tears With Background.  So How Well Does It Actually 
Work?"

Pretty well, overall.  But there are a couple of fairly severe things to 
keep in mind up front.  I discovered early that this is a "chaotic" 
system: 
as a test goes on, it progressively approaches entropy.  And many external 
factors can affect the results; even something as seemingly insignificant 
as the order of the devices in the MIDI chain, or the type/quality of the 
MIDI cables used.

Since timing was the primary function to be tested, I used a computer to 
generate the "Record" and "Loop" cues via MIDI.  This enabled me to loop 
exactly one bar at a defined BPM.  I then programmed a single sidestick 
hit 
(in mono, to make certain the sound was evenly divided between left and 
right channels), and began to count the number of measures it would take 
for the two independent loops to begin drifting noticeably.  Later, I 
reconfirmed the results using a two measure loop, with high-hats on each 
beat, bass drum on beat one of the first measure, and sidestick on beat 
one 
of the second measure.

Listed here are the "worst case" results.  These, by average, also ended 
up 
being the most consistent results, so they're probably what you could well 
expect if you were to put together a similar architecture.  However, it's 
got to be pointed out that every so often (about once every 5-7 tests) I 
would get two loops that would stay in sync almost perfectly for a very, 
very, very long time; they would not drift into a sixteenth or eighth note 
difference for at least 500-700 repetitions of the loop (about the time I 
finally got sick of counting).

So, press 'play'.  I found that once I began a test you could usually 
identify a noticeable drift in phase coherence almost immediately if you 
were using headphones.  This shouldn't really be too much of a nuisance 
unless both channels of the stereo signal are squashed back together into 
mono (and why are you bothering with dual Echo Pros in the first place if 
you're going to squash it all back into mono), which would cause it to 
sound like flanging and phase shifting.  In fact, depending largely upon 
the material, this micro-delay may actually aid stereo separation under 
certain circumstances.

Significant separation or beating between the two loops was not noticeable 
until about 17-20 measures into the test.  At that point, it was possible 
to distinguished the looped sidestick as two distinct hits (a flam, for 
all 
intents).  The two loops fell into an unmistakable rhythmic pattern around 
the 40th repetition, at which time they sounded as two sixteenth notes, 
one 
following immediately after the other.  An eighth note rhythmic pattern 
was 
achieved at approximately the 80th measure, while a full beat (quarter 
note) difference was finally distinguished around measure 150.  In most 
tests, I didn't continue to count further.  By extrapolation one could 
determine that a half-note would fall around 300th loop iteration and a 
complete turnaround of a single-measure loop would happen approximately at 
measure 600.

Following the initial tests, I went back through and performed the same 
experiment using longer loop lengths, as well as performing it under 
different tempos.  I found that these results did not differ dramatically 
from the original test.  I also attempted to repeat the experiment while 
conducting multiple overdubs during the process.  This was to see if 
recording the overdubs would place additional strain on the CPU and affect 
the clock source, therefore causing the units to drift out of sync 
faster.  This likewise resulted in no deviation in the results.

First disclaimer: While I use the term "measure" here, that is only for 
the 
purpose of this particular experiment.  Here, one measure = one repetition 
of the loop.  By no means does the loop have to equal one measure, as it 
could easily be more (or less).  Thus we see that the loops begin to 
become 
rhythmically distinct after about 40-50 iterations.  If the original loop 
is many measures long, then it will simply take that much longer for the 
left and right sides to go out of sync.

Second disclaimer: These results are particular only between my two Echo 
Pros.  We cannot necessarily say for certain what the results would be 
between two completely different Echo Pros, as manufacturing runs on the 
hardware may have used different part lots.  The tolerance of variation on 
these parts may certainly be different from lot to lot.  However, these 
tests should at least give us some ballpark estimate.


"Punch the Magic Button..."

One technique which I found absolutely essential for working with this 
setup is what I call the Loop Realign functionality.  This is something 
I've put together all on my own (as opposed to some explicit function of 
the Echo Pro).  Essentially, it allows you to reset the loop back to its 
original synchronized state, just as if it were freshly recorded.

Setting up a Realign function is relatively easy, provided you've a MIDI 
controller which will allow you to send two MIDI messages in rapid 
succession.  The theory is simple: send a message to stop the loops on 
both 
Echo Pros, immediately followed by another to restart them again.  This 
should reset the synchronization of the two loops back to the state at 
which they began when first recorded.

The Echo Pro allows you to access the Stop and Play functions of the 
Looper 
through MIDI in a variety of methods, including Continuous Controller, 
Program Change, or even via MIDI Notes.  I found using the MIDI CC's the 
easiest for my particular MIDI foot controller (a Peavey PC1600x), and 
thus 
set up a single button/footswitch that would fire off CC #28 with a value 
of 0 (Loop Stop), immediately followed by the same CC with a value of 127 
(Loop Play).  This effectively resets the loops back to their original 
state of synchronization.

There is another issue here to keep in mind as well, though.  If there 
were 
any overdubs later recorded onto the loop while the original loops were 
already out of sync, then those overdubs will be taken out of sync the 
moment you realign the original loop.  Usually there was little noticeable 
effect as long as the base loops were realigned before beginning an 
overdub, or at least when the base loops weren't heinously out of sync 
(like around the 40th repetition) before overdubbing began.

Of course, there are times when realigning overdubs out-of-time can be a 
useful effect in and of itself.  Similarly, If you've dancin' feet, you 
could also use the Realign button in rapid succession to achieve a stutter 
effect on the loop ("ni-ni-ni-ni-nineteen") in much the same manner as 
samplers abused such functionality over two decades ago.


"Okay, Break It Down For Us..."

So all the test methodology and results aside, how well does it work 
*musically*?  Obviously, for the test, I wanted to use sounds and material 
that would most strenuously point out the strengths and flaws of the 
setup.  But now we have to inquire
how well the architecture performs with real musical content.  In that 
respect, I've got to say that, frankly, I'm really quite pleased.

Rather than just using sidesticks and sharp percussion hits -- as I did in 
the lab -- I've now spent a few nights actually playing and looping the 
Morpheus with the dual Echo Pros.  In using various sorts of content 
(pads, 
leads, comps, guitar emulations, tuned percussion, effects, etc.), I've 
yet 
to come across a situation where the synchronization issues have really 
given me fits.  In fact, in most cases where I eventually hit the Realign 
button, I've actually been less pleased with the tightly-synced loops than 
I was when they had drifted ever so slightly out-of-sync.  In many cases, 
the drift does seem to somewhat enhance the stereo imaging without 
completely botching the timing.

I was even able to consistently yank both units down to half-speed and 
back, reverse them, overdub, revert the loops to normal, then do it all 
over again and again in any order.  The loops and their content stayed as 
tight as if I'd merely left them to repeat normally.  Sweet!

Further afield, there's still plenty with which to experiment in this 
setup.  For instance, everything we've discussed so far has taken for 
granted that the parameters on each unit match each other exactly.  But 
what if we set the internal delay's parameters for Time, Feedback, and/or 
Echo Modulation differently on each unit?  Or what if we intentionally 
split and varied the content going into each Echo Pro, so that it is truly 
two mono streams?  Finally, one trick which has been pointed out is the 
fact that the 1/4 inch and XLR inputs/outputs for the Echo Pro are all 
active simultaneously.  There have been some interesting results that have 
occurred when others have cross-connected between the two units though the 
jacks not used for standard I/O.

In conclusion, I've found that implementing dual Echo Pros to be a much 
more viable solution than I'd believed it could be when I first began 
researching this idea.  It gives one the immediacy and simplicity that 
people have come to appreciate from using the Line 6 Loop Sampler 
algorithm 
in either the DL-4 or single Echo Pro, as well as better quality input and 
output (compared to the DL-4), more user presets, and most importantly 
*stereo* implementation of the looper.  This is invaluable to those of us 
for whom stereo is not just a nice "extra", but is indeed a core 
requirement.

When I started this, I was hoping merely to solve a major annoyance with 
my 
secondary looper in relation to my Repeater.  Now, in the end, I find that 
by solving that problem I've constructed a completely viable 
stereo-looping 
setup in its own right.

         --m.

_____
"i want to reach my hand into the dark and *feel* what reaches back"
                                                 -recoil