Sound-devices 722 User Manual download pdf (Page 22)

722 User Guide and Technical Information

v. 2.67 Features and specifications are subject to change. Visit www.sounddevices.com for the latest documentation.

The 722 has 24 bit analog-to-digital converters. To obtain 16 bit recording the 722 can be set to dither

24 bit digital signals to 16 bit. The 722 uses a proprietary pseudo-random dither routine for accurate

bit rate reduction. Dither can be defeated in the user menu. Without dither, 24 bit audio is truncated

to 16 bit, meaning the least signiﬁcant 8 bits are discarded.

Once a ﬁle is recorded its sampling rate and bit depth can not be changed in the recorder. The 722 does

not perform sample rate conversion or bit depth changes. File conversion must be done in another en-

vironment, such as an audio workstation. Alternatively, a real-time analog transfer is often performed

instead of sample rate conversion.

Word Clock

Stable word clock is fundamental to high quality a digital audio signal. The 722 uses a highly-stable

crystal to generate its internal word clock frequencies. The 722 can clock external devices from its

word clock and accept external clock sources for recording.

The 722 disregards external clock, both AES and word clock, during playback.

Clock Master

When sending digital audio to several devices, one unit is designated as the word clock master and

the others as slaves. Generally, the device with the analog-to-digital converter is designated as the

word clock master.

The 722 can function as an A/D converter and can be used as the master word clock source. Slaved

devices will derive their word clock timing from either their digital audio inputs, S/PDIF or AES/

EBU, or through their word clock input connection. As a word clock master the 722 generates word

clock whether or not audio is sent.

Clock Slave

When using an external digital preampliﬁer connected to the 722 inputs, the recorder can derive its

clock signal from the AES (S/PDIF) stream (it will slave to the external device), or the external device

can be slaved from the 722 (if the external device has word clock input or accepts clock from the

722’s digital output). If, for example, you are using a wireless receiver with a digital output, it may

not have an external word clock input, and will be the word clock master.

If digital audio is connected to the 722 from more than one digital device, you must word clock the

sources to the same clock, otherwise variations between the sources will render their signals unus-

able.

If the 722 is slaved to external word clock, be certain that the source is stable. Loss of the word clock

signal during recording can cause the 722 to revert back to its internally set sampling frequency. If

this occurs, the portion of the ﬁle recorded after the loss of word clock may not play back at the prop-

er speed. For reliability, set the 722 to the same sample frequency as the word clock source. Loss of

the word clock signal in this case will likely cause a glitch in the ﬁle, but the ﬁle may still be usable.

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Sound-devices 722 User Manual Page 22