MACKIE HDR24/96 - Manual (Page 213)

HDR 24/96
Inputs and Outputs
TheDIO-8 has two sets of connectors, a pair of Lightpipe fiber optic TOSLink connectors and a
25-pin D-subminiature connector used for the TASCAM multichannel digital interface on DTRS
recorders. In addition, it has a BNC connector, which provides a DTRS clock output for devices
that require it. The DTRS clock is the same frequency as the word clock, but is 90 degrees out of
phase with the standard word clock.
The Lightpipe connection works in the same manner as that on the OPT-8. When connecting to
an ADAT, set the ADAT to receive its clock from the digital input, allowing the HDR24/96 to be
the clock master.
Even if you’re copying from the ADAT to the HDR/2496, you must connect both the input and
output Lightpipes so that the ADAT will receive the clock signal from the HDR24/96.
When using the DTRS I/O connector, set the DTRS recorder to External clock and use the SYNC
output of the first DIO-8 (not the Word Clock output) as the DTRS clock source.
Signal Polarity
Because the DIO-8 card was designed for compatibility with the original ADAT, it inverts the
polarity of the incoming signal. This means that a positive-going waveform coming into the card
will be recorded on disk as a negative-going waveform. When playing back through the DIO-8
card, the signal goes through a second polarity inversion, so you get out what you put in. OK so
far. But there are a couple of situations where this can cause you some extra bookkeeping and
manipulations.
Suppose your recording path is as follows:
Microphone A/D converter with Lightpipe Output DIO-8 –HDR24/96.
Now, you move the project over to your DAW for final editing, processing, and mixing. You
FTP the files over and you have audio with inverted polarity on your computer. Everything you
hear when playing the project on your DAW will have inverted polarity. Your mix will have
inverted polarity, and if you burn CDs from your mix, they will have inverted polarity.
Another place where polarity confusion can occur is if you have an assortment of DIO-8 and
OPT-8 cards, perhaps DIO-8 cards installed in your Mackie d8b console and OPT-8 cards in your
HDR24/96. Polarity gets inverted going from the console to the DIO-8, and the OPT-8 in the
recorder maintains that polarity, causing an inverted version of the audio to be written to disk.
When mixing, the inverted audio comes out of the OPT-8 still inverted, then gets turned right side
up by the DIO-8 on its way into the console. So far, so good.
But suppose you bypassed the console when you recorded a few tracks, say going from an
outboard mic preamp with a Lightpipe output directly in to the recorder’s OPT-8 card. Those
tracks don’t have their polarity inverted yet. But when you mix, they’ll make a trip through the
DIO-8 on their way into the console, and they’ll be inverted while your other (console-recorded
tracks) are not.
Does audio polarity inversion matter? Not always. It would definitely matter if you had a stereo
pair of tracks and inverted one, but not the other. And certainly there are plenty of listeners out
there who have their speakers hooked up backwards and listen to audio with inverted polarity all
the time. On certain program material, polarity inversion is impossible to detect by ear, but on
some material, it’s easy – that’s why polarity switches on a console are such a useful thing.
The cure is to keep track of your signal path, make note of when you need to invert polarity to get
back to what was coming into the microphone, and use those polarity switches where necessary.
Technical Reference 213