MOTU 896HD User's Guide download pdf (Page 29)

INSTALLING THE MOTU 896 HARDWARE

Figure 4-14: When transferring audio without sample rate conver-

sion, two devices must have phased-locked audio clocks to prevent

clicks, pops or other artifacts.

Without sample rate conversion, there are two ways

to achieve phase lock: slave one device to the other,

or slave both devices to a third master clock. If you

have three or more digital audio devices, you need

to slave them all to a single master audio clock.

Figure 4-15: Without sample rate conversion, you need to choose a

clock master to which all other devices slave. Each slaved device

remains continuously resolved to the master, meaning that there will

be no drift over time.

Audio phase lock as shown above in Figure 4-15

can be achieved independently of time code

(location). For example, one device can be the time

code master while another is the audio clock

master. But only one device can be the audio clock

master.

Another beneﬁt of direct master/slave clocking

(without sample rate conversion) is that each

slaved device remains continuously resolved to the

master, which means that there will be no gradual

drift over time. This form of synchronization is

best for audio that needs to remain resolved to ﬁlm,

video, etc.

Sample rate conversion

With sample rate conversion (SRC), an extra level

of master/slave clocking is added to the equation,

as demonstrated below in Figure 4-16, which

shows the clocking going on when you transfer

digital audio from the 896 (AES/EBU OUT) to a

DAT deck (AES/EBU IN) using SRC. Notice that

with SRC, the DAT deck is not slaved to the 896’s

system clock. Instead, their clocks are running

completely independently of one another. But also

notice that the DAT deck must still slave to the

sample-rate-converted output from the 896 for a

clean digital audio transfer (unless it has its own

rate converter on its AES/EBU input).

Figure 4-16: Clock relationships when sending audio from the 896 to

a DAT deck using sample rate conversion. The DAT deck needs to be

slaving to its AES/EBU input. *Note: the 896 AES/EBU output can

actually be clocked from a number of different sources. In this

example, it is resolved to the 896 system clock. For details about other

possible clock sources, see “Clocking scenarios for AES/EBU output”

on page 30.

System clock, AES clock & rate convert settings

When you are setting up AES/EBU input and

output with the 896, pay careful attention to the

following settings in the MOTU FireWire Audio

Console (see the quick reference overview on

page 7):

■ Clock source

■ Sample rate conversion

These options are mentioned brieﬂy in the

following sections. For further details, see “Clock

Source” on page 36 and “Sample Rate Conversion”

on page 39.

Not phase-locked Phase-locked

Device A

Device B

Master

Slave

Master

Slave Slave

896 master clock

Input

clock

Output

clock

896 Sample

Rate converter

(slaves to 896 SRC output clock)

(master)

(slaves to 896 master clock)

DAT deck

(master*)

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