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Looper's Delight
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Kim, all I can say is that this is really useful, specific information... and that I hope Electrix sends you a check for doing their beta testing for them... I haven't done any MIDI syncing yet, but this should've been caught before release. Kevin > sorry for copying the mail below whole, but it was from a while ago so I > figured the context was needed again. I was concerned about this problem > quite a bit, and one of my reasons to get a repeater was just to figure > this one out. (how's that for dedication? :) > > Anyway, it is true that when you try to sync an Echoplex to the > Repeater's > midi clock out there will be problems. The Echoplex loop time ends up > slightly longer than the Repeater, and then shifts against the Repeater's > loop as they play together. I thought this was really weird, since I had > never seen anything like it with the EDP. > > I did some analysis of the Repeater's midi clock output, and sure enough > there is a subtle bug in the Repeater clock out. > > If you aren't familiar with how midi clock works, basically it uses the > ancient 24 pulses per quarter note method that dates back to the days of > analog synths. in midi though, the "pulses" are actually a particular > System Realtime byte. The clock generator sends 24 of these per > beat at the > given tempo. The clock pulses are normally spaced evenly in time so the > receiver can use whichever pulse it needs to time most any sort > of rhythm. > so the time interval between these clock pulses should be equal to 1/24th > of a beat. > > I made a little max patch that times the interval between midi > clock pulses > in milliseconds, and saves the data it collects into a text file. > With the > Repeater clock, I see the 23rd pulse of every beat is delayed by > an entire > interval. The 24th pulse then comes immediately after that, with no > interval at all. so the 23rd pulse is practically right on top of > it. So if > the tempo is 125 BPM, the usual interval between pulses is 20ms. Between > the 22nd and 23rd pulses the interval is 40ms, and between the 23rd and > 24th pulse is less than 1ms. (Max says the delay is 0ms between these, > since it resolves to 1ms.) That means these last two pulses in > the beat are > as close together as two midi commands can be. > > The echoplex apparently decides this situation of two clock > pulses so close > together and completely different from all the other pulses is nonsense, > and doesn't count one of them. It counts the first pulse in the next beat > as the 24th pulse. So it ends up thinking the beat is 1/24th of a beat > longer than the Repeater thinks it is. This is why a 2 bar loop at 120BPM > shows as 4.1 seconds long on the EDP instead of 4.0 seconds. > > I tried the midi clock outputs from some other devices into my > max patch to > get some comparison data and they did not have any problem like this. All > the pulses were evenly spaced as they should be. > > My guess is, this delayed pulse also why drum machines and sequencers > synchronized to Repeater's midi clock out sound a little wobbly, even > though they don't always get off so much like the echoplex does. > Some notes > probably get shifted around a little while it tries to sort the > weird clock > pulses out. > > hopefully electrix fixes this one quick, since it is really a drag. The > only work around I can see here is either use something else for a midi > clock to both Repeater and EDP, or slave the Repeater to the EDP > midi clock > out. > > hope this helps, > kim