Recording - December 2015 - 61

(although not on audio tracks), but some
old gear will have Tape Sync I/O for FSK
(Frequency Shift Keying) timebase, with or
without embedded "smart" signals that
convert to SPP information.
Sync-Latching: bridging the realms of
Songs and Patterns
Sync-Latch is a term originally coined by
Mutable Instruments' founder and designer
Olivier Gillet, although the concept has
been around without a name for decades.
Sync-latching is an advanced synchronization method whereby timebase is maintained between devices, but transport
(START / STOP) signals are deferred to precise musical boundaries-typically to the
next bar of music or a pattern loop point.
This requires the sync-latching control device
to discern which timebase (MIDI) clock ticks
are on the beat, a bar line, or other contextual boundary. See Figure 5.
The basic mechanism of sync latching
can be found in other products, too. For
example, the Innerclock Systems DAW plugin, upon reception of Play transport, waits
until the next measure mark before sending
out timebase to its dedicated hardware.
The Innerclock Systems Sync Gen II
POro, SND ACME-4, Expert Sleepers
USAMO, and Elektron Overbridge are
all pointing to a bright future where DAW
and hardware seamlessly integrate for a
smooth work experience.
Other forms of sync: LFOs and arpeggiators
What if you just need a beat-synched LFO
generator to control external synths, either
via MIDI Control Change messages or control voltages... say, to have tremolo in time
with your song? The new Roland SBX-1, the
Kenton Pro-Solo, or the Koma RH301 would
be your best bet. You could also use the
Expert Sleepers gear mentioned above.
Arpeggiators are a special case. Old
vintage synths would have arpeggiators
that followed trigger signals: one trigger,
one step. Vintage drum machines might
have trigger outputs tied to one instrument. For example, the Rimshot channel
on the Roland TR-707 would send a trigger every time a Rimshot would play,
which in turn could step through an
arpeggiator, producing syncopated patterns. Sometimes a timebase signal could
be divided down to run an arpeggiator;
dividing 24 PPQN by 6 gets you 4
PPQN, or 16th notes.
With MIDI sync, arpeggiators are a huge
can of worms. Not only must you deal with
latency and jitter, but every arpeggiator
responds differently to external MIDI clocks!
You have to know if an arpeggiator syncs
to the first key played, or to a beat or bar
line (often based on seeing a MIDI Start or
Continue message), or triggers timesynched loops or phrases rather than notes,
with or without SPP compliance.

Clever sync hacks
Sometimes you just need to improvise
sync with your existing gear. Here are
some tricks that might help you.
If your computer system's interface has
any extra audio outputs (beyond the
usual stereo pair), then you can create
short WAV files of rectangular trigger /
clock pulses and place them onto your
DAW timeline. In this way you force the
DAW to directly output the desired timebase or triggers, which get independently routed out one of your audio interface's
spare outputs. This pulse sample should
contain a rising rectangular edge, immediately going from zero to full-scale positive value, where it holds for at least 10
ms and drops to zero, where it stays for
at least 15 to 20 ms.
These pulse wave samples can be placed
on your DAW grid according to the timebase needed on the external instrument. For
example, use 4 PPQN to drive a Roland
Juno 60's arpeggiator at 16th note resolution. If you want to directly drive a drum
machine like the SCI TOM or Drumtraks via
their Ext. Clock inputs, then you'd place the
samples at 24 PPQN. In either case, these
machines are driven jitter-free.
Now these signals will likely need level
amplification and possibly DC-coupling,
in order for them to be properly recognized at the vintage hardware's clock or
trigger input. Typical audio signal levels
are AC-coupled and never reach beyond
2V. Vintage Trigger and Clock inputs are
expecting DC-coupled +5V levels or-as
found on really old synths-voltages as
high as +15V. However, in the cases of
the SCI TOM/Drumtraks or the Kawai R100, audio levels are sufficient.
Yet another low-tech way of using an
auxiliary audio port as a clock output is
synthesizing FSK or even Smart FSK directly from a DAW track. Software maker RV0
has a series of DAW plug-ins which generate standard FSK (via 'Sync Unit AC') suitable for slaving a Roland MC-202, MSQ700, MC-500, or a Korg KMS-30 via their
'tape sync jacks'. Similarly their other plugin, Sync Unit DC, generates (unmodulated)
timebase for output at an aux audio channel. Visit http://www.rv0.be/sync-unit for
more info.
Lock it in
Understanding timebase and transport
will allow to you to solve basic setups
without buying expensive converters or
sync boxes. With this knowledge in hand,
you can also know when and how to add
sync hardware if you need it, and understand why your grooves don't groove.
Have fun!
Michael Lauter (lauter@recording
mag.com) is an independent digital video
producer, filmmaker, and soundtrack
composer, living in Denver, CO.
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http://www.rv0.be/sync-unit http://www.placidaudio.com

Table of Contents for the Digital Edition of Recording - December 2015