system sampling rate, from wherever it is derived, or sample rate conversion must be enabled.

The digital outputs are at the system sampling rate, and all analog to digital and digital to analog conversion is done at the system sampling rate.

S/P DIF

The digital inputs 1/2 are received at either the AES/EBU 1/2 input jack or the S/P DIF 1/2 input jack. To select between the two, use the DIN 1/2 parameter on the "bottom" inputs menu page in the SETUP area.

The digital outputs 1/2 are sent out at both the AES/EBU 1/2 output jack and the S/P DIF 1/2 output jack. To select between the two formats, use the DOUT 1/2 parameter on the

"bottom" format menu page in the SETUP area. To be clear, signals will be present at both the AES/EBU 1/2 output and the S/P DIF 1/2 output, but they can only be one format. S/P DIF selects a "consumer" format while AES/EBU selects a "professional" format. Use the AES/EBU format unless you have a compelling reason to do otherwise.

Note: The digital inputs 1/2 need not be assigned to the same protocol as the digital outputs 1/2. In other words, digital inputs 1/2 can be received at the AES/EBU 1/2 input jack and digital outputs 1/2 can be sent via the S/P DIF protocol, or vice-versa.

Similarly, on the H8000FW, S/P DIF inputs 3/4 can be used in place of AES 11/12. Their protocols are fixed.

See DIN 11/12 allows the choice of either AES/EBU or S/P DIF for AES11/12. on page 61.

SAMPLING RATES

The H8000FW can operate over a range of sampling rates, from 32kHz to 100kHz. Because the higher sampling rates demand more of the signal processing resources, some large presets will not operate at the higher rates. These are identified by the absence of the "96" symbol.

If one (or two) of these large presets is loaded, the H8000FW will not allow Int 88.2 or Int 96kHz to be selected and will not lock to any digital source above 50kHz. It may be necessary

to unload both A and B presets before a higher sampling rate can be selected.

Similarly, if one of these higher clock rates is selected, or the system is locked to a digital

source above 50kHz, the H8000FW will not allow these larger programs to be loaded. 79

In effect, the H8000FW has two "speeds," a bit like gear ratios on a car. In the normal (lower) speed range, all presets can run, but only sampling rates between 32kHz and 50kHz may be used.

In the higher speed range, some presets cannot run (those which do not have the "96" symbol beside their name on the program screen (e.g., Quad*16 Grafic Eq and Stereo*32 Grafic Eq in this screen shot), but the whole sampling rate range may be used.

Note that because the ADAT protocol does not support the higher sampling rates, ADAT inputs and outputs are unusable at 88.2kHz and 96kHz on the H8000 and H8000A.

The H8000FW (but not H8000, H8000A) supports the SMUX protocol, allowing the ADAT inputs to pass four channels at 96kHz.

The System Sampling Rate – A Digital Audio Primer

All digital audio systems operate by expressing the value of the audio signal at any instant in time as a (digital) number. This number is sampled (recalculated) at regular very short intervals. The rate at which the value is sampled is known as (wait for it) the sample rate, sometimes known as a clock.

All the internal parts of the H8000FW family (including the A/D and D/A converters and the digital outputs) run at a single sample rate, known as the system sampling rate. This rate may be determined either by an internal clock, or by a single external input. If any external input is used as an audio source, it must have exactly the same sample rate as the system sampling rate, or things will get out of step, causing one or more of the digital values to be lost. This will result in clicks or distortion – a bad thing. For example, at a sample rate of 96kHz, an 0.001% difference (10 parts per million – more accurate than most clock sources) will cause a (probably faint) click about every second.

A very small difference in sample rates, as in the example above, results in slipping, meaning that the sample points “slip” past each other in time. Depending on how severe the sample rate difference is, the results may be inaudible (slight clicks will be ‘masked’ by the signal) but will be avoided by all those interested in audio quality.

Since it is unlikely that pure chance will allow any two or more external signals to have exactly the same sample rate, it is necessary to synchronize (lock) them, meaning that the external signals derive their sample rate from some common reference. This may be either a signal from the H8000FW itself, or an external signal feeding the H8000FW. It is good

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