HHB comm CDR-882 Advanced Features & Operation, Internal & External Clocks, Clock Source Display

Advanced Features & Operation

Advanced Features & Operation

Internal & External Clocks

Word clock in the CDR-882 can be obtained from several sources. An internal crystal oscillator is provided, which is the preferred source for use with analogue input signals. When digital input signals are used, the word clock may be extracted from the AES/EBU or S/PDIF bitstreams themselves. A further option is to use a separate external clock signal.

In many professional digital audio systems, a separate external master clock is used to synchronise all digital audio equipment in the system; the CDR-882 is provided with an external word clock input for use in such a situation.

Clock selection in the CDR-882 is normally automatic, the source being selected to suit the audio input being used. The following rules apply to the automatic selection system:

•If an analogue input (Balanced or Unbal) is selected, the CDR-882’s own internal clock will be used

•If a digital input (AES/EBU, S/PDIF Coax or Optical) is selected, the signal itself will be used as the clock source, as long as it is within the acceptable frequency range, namely 44.1kHz +/-100ppm

•If a digital input is outside this range the internal clock will be used, and the input signal sample rate converted to the internal clock frequency

The choice of the internal clock for analogue inputs or the embedded word clock for digital inputs will give perfectly satisfactory results in most recording situations. However, it is possible to override the automatic selection described above and use a different word clock source.

The Clock submenu is used to select a different word clock source from that chosen automatically. See page 31 for full details.

Overriding the automatic selection allows the user to:

•Use either an external master studio clock or a digital audio signal (AES/EBU or S/PDIF) as word clock source when using analogue inputs. This may be desirable for all but the simplest digital audio systems as it ensures that the clocks of all interconnected equipment are in exact synchronisation

•The external clock may be derived from a dedicated generator, in which case it will be applied to the rear BNC connector and Wordclock selected as the source in the menu. Alternatively, “digital silence” can be used in the form of an AES/EBU or S/PDIF signal without audio content; in this case, Digital Input is selected as the source and the appropriate input connector used. Whichever inputs are being used, an external word clock input must meet the CDR-882’s frequency requirements of 44.1kHz ± 100ppm

•Use an external master studio clock as the word clock source when using the CDR-882’s digital inputs. Again, this will be connected at the Word Clock input and Wordclock selected as the source. In this case, the word clock connected to the CDR-882 must also be connected as an external clock to the source of digital audio

•Use the CDR-882’s internal clock source with digital inputs. This situation will occur when the CDR-882 is the clock master in a system. A typical scenario would be where the digital output of a semi-professional PC sound card is feeding S/PDIF to the corresponding inputs of the CDR-882. In such a case, it is likely that the CDR- 882’s internal clock’s stability will be better than that of the sound card’s. The CDR-882’s digital outputs can be connected to the inputs of the sound card, to be used as its clock. The CDR-882 thus acts as the master clock source

Clock Source Display

The front panel LCD always indicates the currently-selected word clock source, whether the selection has been made automatically or manually.

•Internal - the internal master clock

•DIG - an AES/EBU or S/PDIF digital audio signal at the appropriate rear connector

•WCLK - a word clock signal applied at the rear BNC connector

If external word clock is selected, and the applied clock signal has a frequency outside the range 44.1kHz +/-100ppm, synchronisation is not possible and the WCLK indication will flash. Similarly, if Digital Input is selected, and the applied signal has a clock frequency outside this same range, synchronisation will not be possible and DIG will flash. In these cases, the problem will need to be resolved before a recording can be made, either by correcting the clock frequency of the external source or by selecting Internal or Auto instead.

38 www.hhb.co.uk CDR-882 User Manual Version 1.0