Lexicon PCM 42 - 4.3.2 Interfacing Clock with Rhythm Machines

desired here is ‘1°. Experiment with this button, obser-
ving the rate of the CLK lamp, then return to 4 value o
ne via en fi ary ishec.
VW HSOeC
Another way to think of the clock ratios is in terms of
rnusical notation. f the delay memory Size 's considered
to be equal to one bar of music, then the clock intervals
ray be expressed in the familiar forms of half-notes,
CLOCK PULSES
quarter notes, eighths, etc. Fhe different values for the
numerator of the fraction can be consi idered 0 be tes
between notes. For instance, the clock ratio i? can
pe expressed as in Fig. 4.6-a and a value of ° 1/4 asin
4 6-D. ihe ratio 3/16" 1s depicted as three sixteenth
notes in Fig. 4.6-c. In actual practice, the loop length
will often be equal to two, four, or eight measures.
Simply expand the note values to fit the context of
Temipo.
| CLOCK SETTING |
Figure 4.6 — THE MUSICAL VALUES OF SELECTED CLOCK RATIOS
One measure represents the length of the maximum available delay time; the notes or ties span the length of the inter-
val between clock pulses.
4.3.2 interfacing the Clock with Rhythm
Machines.
The Clock Output may also be used as a clock signal
for many types of sequencers and electronic rhythm
units. Most modeis of synthesizer sequencers provide
an external clock input. All that is needed in most cases
is to patch the PCM 42 CLOCK OUTPUT jack to this ex-
ternal clock. Some models (e.g. Moog) use 1/4” phone
jacks and some (Arp, Oberheim) use 1/8” mini-phone
jacks. In a few cases, the +5 voit output of the PCM 42
will need to be boosted in order to provide enough
signal for the sequencer. Consult the manufacturer's
literature if you have any problems.
Once the user’s sequencer is connected to the PCM
42, the CLOCK OUTPUT may be programmed to drive
the sequencer at the rate desired. if the sequence out-
put is now fed.through the PCM 472, it will be found that
the note intervals synchronize perfectly into the delay
loop length. By using FEEDBACK and INFINITE
REPEAT, avery tight, locked-in feeling can be obtained.
if the sequence or rhythm pattern is played back
22
without processing, and a lead or rhythm instrument is
played through the PCM 42, the instrument can be used
i ke another sequencer in paralle with the first. Working
in this fashion, and with the loop techniques described
in Section 4.2, some remarkable textures and effects
can be generated.
The Clock Output may aiso be interfaced to ANY
automatic drum unit which provides an external clock
input. A number of lower-cost units do not provide this
feature, but in many cases it is possible to modify the
unit slightly to accommodate it. Consult the manufac-
turer for information. In many cases, the unit will be set
up to operate with an odd subdivision of the meter such
as 24 or 48 clock pulses per quarter. This is not a prob-
lem providing that the PCM 42 clock input is also used
during the programming. of the beat. All that will be lost
is some of the triplet divisions of time. In programming
rhythms on a system set ob in this fashion, it is useful to
first program a kick drum beat at the quarter note rate to
establish the bar length. Then enter the rest of the
rhythm, erasing the initial reference beat if necessary.