Apogee AD-8000 Specifications download pdf (Page 17)

Once a sync source is selected, the processor measures the sample rate and sets the sample rate LEDs

appropriately. The measurement is accurate to one part in 2000, so that a “pulled” rate can be distinguished

accurately. For example, 47.952 kHz can be distinguished from 48 kHz. The processor disables invalid sync

selections—selecting 44.1 when the external sync source is at 48 is not allowed, for example.

If digital input sources are selected, but the detected clock for that input is out of sync with the selected

sync source, or there is excessive attenuation or jitter, or some kind of encoding error in the incoming digital

audio is detected, then the ERROR LED will illuminate indicating a digital locking problem. This will cause pops

and clicks in the audio, or in the worst case, the AD-8000 will mute.

If the digital source material is being received correctly and the low jitter clock is locked to it, then the

microprocessor turns on the LOCK LED and un-mutes the audio. If the AD-8000 is being synchronized with a

varispeeding source, or is synchronized to a non-standard sample rate, the sample rate closest to the current

sync source sample rate will flash and the LOCK LED will remain on.

The AD-8000 retains information on analog sync sources. Whenever the inputs are all analog, the current

sync source is saved. If at least one input is changed to digital, the sync source is changed to the correspond-

ing digital sync source. If all inputs are restored to analog, the “last analog sync source” is enabled, even if sync

sources were changed while digital inputs were being used. On power up, the default analog sync restore state

is 48 kHz internal crystal.

Video Module Sync Options

The video module is a separate, optional board which is plugged into a socket on the main digital board. If

present, the video module enables the video sync options, as well as “pulling” external sync by 0.1%.

The video module accepts either video horizontal sync pulses (PAL, NTSC, or 60 Hz monochrome) or FS

(word clock) from any one of several sources (as selected on the main board), and generates FS, FS x 1.001, or

FS ÷ 1.001 (pulled FS).

Video Sync and Sampling Rates

Video Horiz. Sync. Sample Rate(s)

60 Hz 15.75 44.056, 44.1, 44.144, 47.952, 48, 48.048

NTSC 15.734 44.056, 44.1, 44.144, 47.952, 48, 48.048

PAL 15.625 44.056, 44.1, 44.144, 47.952, 48, 48.048

WC N/A Any

XTAL N/A 44.056, 44.1, 44.144, 47.952, 48, 48.048

Locking to a Video Sync Source

Locking to a video sync source is very straightforward, thanks to the mediation of the microprocessor. All

that has to be done is to select VIDEO as the sync source, and then select the desired sample rate. The micro-

processor measures the video horizontal line rate, determines the type of video from that measurement, and

configures the video module phase-locked loops to multiply the line rate by the appropriate ratio to get the

desired sample rate.

Pulling Any Sync Source by 0.1%

The video module also makes possible adjusting any sync source, including the 44.1 or 48 kHz crystal, by

0.1% up or down.

Sync Source Selection

Standard synchronization sources are AES, S/PDIF, word clock, and crystal. Optional synchronization

sources with the video module are PAL, NTSC, and 60 Hz video. Additional digital audio sync sources are avail-

able through use of the AMBus.

The microprocessor determines which optional modules or cards are plugged in and enables those selec-

tions if they are available. Additionally, if the video module is plugged in, then it will also identify the type of

video from the measured horizontal sync rate (15.75 kHz = Mono 60 Hz, 15.734 kHz = NTSC, and 15.625 kHz

= PAL) and set the NTSC, PAL, and Mono LEDs accordingly.

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AD-8000 Operating Manual

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Apogee AD-8000 Specifications Page 17

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