studio practice to establish a central high quality clock source, to which all the digital audio equipment is synchronized, usually by Word Clock.

The H8000FW family’s digital inputs AES1-4 (and AES5-8 on the H8000) incorporate optional sample rate conversion, where new digital values are “made up” to fill in the gaps caused by a difference in sample rates.

Using the Internal Clock

When you use the "internal" clock, the system sampling rate will be that of the internal clock. Unless sample rate conversion is on ("bottom" page under clock in the SETUP area), slipping will

occur on any digital inputs unless they are externally locked to one of the H8000's digital outputs. The ADAT (and AES11-18 and FireWire on the H8000FW) inputs have no sample rate conversion and thus cannot be used with an internal clock unless the external unit is synchronized to the H8000FW's digital outputs.

See The Status of The Digital Inputs When Using the Internal Clock on page 82.

Selecting the Internal Clock’s Rate

To select the internal clock, set the Source parameter on the clock menu page in the

SETUP area to Int 44.1 kHz, Int 48.0 kHz, Int 88.2 kHz, or Int 96.0 kHz:

44.1 kHz The rate of standard compact disks. The "44.1kHz sample rate indicator" is illuminated. The highest reproducible audio frequency is ~20kHz.

48 kHz The "professional" or "broadcast" rate. The highest reproducible audio frequency is ~22kHz.

88.2 kHz Twice the rate of standard compact disks. This raises the highest possible reproducible audio frequency to ~40 kHz. The cost of these "20k +" overtones is a reduction in the size of the programs the H8000FW can run. Some programs will be "unloadable" when 88.2 kHz is selected. Similarly, if one of these programs is loaded, you will not be able to select 88.2 kHz.

96 kHz The current "professional rate," commonly used in DVD production. This raises the highest possible reproducible audio frequency to around 44kHz. Some programs will be "unloadable" when 96 kHz is selected.

The actual value of the system sampling rate can be read in the field that reads, "Sample Rate: xxxxx." This will be accurate to the nearest Hz.

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Of course, if you select one of the fixed rates (44.1 kHz, 48 kHz, 88.2 kHz, or 96 kHz), the actual rate will be the same as the rate you select.

Note that when an H8000FW is connected by FireWire to a running computer, the Source parameter cannot be changed – you should change it from your DAW or other application to be sure that they remain the same. They may also be changed from the computer Control Panel, but this may cause trouble with some applications.

See Miscellaneous Setup Options on page 138 for other sync options.

The Status of The Digital Inputs When Using the Internal Clock

When using the internal clock, the sampling rates of the signals at the digital inputs must be exactly equal to that of the internal clock (unlikely) or sample rate conversion must be turned on under the "bottom" clock menu page in the setup area.

The upper right-hand side of the clock menu page in the SETUP area displays the status of the digital inputs. DIN 1/2 reflects the status of the digital inputs 1/2 (either AES/EBU 1/2 or S/P DIF 1/2 depending on DIN 1/2 on the inputs menu page). DIN 3/4 reflects the status of the digital inputs 3/4 and so on. Not surprisingly, ADAT reflects the status of the ADAT input.

The status of the digital inputs will be

slipping signals are present, but their sampling rate is close to but not locked to the system sample rate. As described above, this may cause clicks or distortion. When the external signal is very close to the internal rate, the status indicator may flicker between slipping and OK. Some slipping may be acceptable for monitoring or other non critical applications, but in general, the greater the difference between the system sample rate and that of the digital input, the greater the distortion. Of course, you can always just turn on the sample rate converter for the AES/EBU 1-4 and S/P DIF 1-2 inputs. No sample rate conversion exists for the other external inputs so these should not normally be used if slipping.

OK signals are present, and their sampling rate is locked to the internal clock rate. All is good !

unlocked either no signals are present, their sampling rate is very unstable, or something is dreadfully wrong with them.

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If the words slipping or unlocked are in parentheses (as shown above for the ADAT inputs), this means that the respective inputs are not routed (not connected to any inputs and hence unused) and that the indication can be ignored.

Understanding the "System Sampling Rate and External Sync Indicator" When Using the Internal Clock

The "System Sampling Rate and External Sync Indicator" is the box of five LEDs immediately to the left of the display. The top four LEDs indicate the status of the system sampling rate:

Solidly Lit: When one of the top four LEDs is solidly lit, the system sampling rate is exact (+/- 0.05%) (the LED corresponding to the system sampling rate will illuminate).

Blinking: When one of the top four LEDs is blinking, the system sampling rate is between one of the fixed rates (the LED corresponding to the nearest sampling rate will blink).

Of course, if you select one of the fixed rates (44.1 kHz, 48 kHz, 88.2 kHz, or 96 kHz), the LED corresponding to your selection should light solidly.

The bottom LED, EXT, has four possible states:

Not lit at all: When the bottom LED is not lit at all, none of the digital inputs are routed. This would happen only if the DSP A and DSP B inputs and the main outputs were either unconnected or only connected to the analog inputs - no digital signals whatsoever!

Solidly lit: When the bottom LED is solidly lit, the sampling rates of all routed digital inputs are locked to the internal clock rate and all is good. This should be the normal state.

Blinking regularly: When the bottom LED is blinking regularly, at least one (and maybe more than one) routed digital input is unlocked.

Use the right-hand side of the clock menu page in the SETUP area to see which digital inputs are in fact unlocked. As before, you can ignore those in parentheses ( ).

Blinking irregularly: When the bottom LED is blinking irregularly, at least one (and maybe more than one) routed digital input is "slipping" relative to the internal clock. Use the right-hand side of the clock menu page in the SETUP area to see which digital inputs are in fact slipping.

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