MACKIE HDR24/96 - Manual (Page 210)

HDR 24/96
Sorry, the lasers aren’t color coded so you’ll still have to figure out which group of 8 channels
you have in your hand.
Signal Polarity
Signal polarity is preserved through the OPT-8. If it appears that you have an inverted signal it’s
possible that there’s a mis-wiring or polarity inversion with your outboard A/D or D/A
converters.
Be aware of one other polarity issue however. The original ADAT (often called the “blackface”
because later models had silver front panels) inverts the signal polarity in its A/D converter and
inverts it back to normal in its D/A converter. If you’re transferring a recording that was made
via the analog inputs of an original ADAT into the HDR24/96 through the OPT-8, since the
signal polarity on the tape is inverted, it will be inverted on the HDR24/96.
It doesn’t matter whether you’re playing the tape on a new or an old ADAT (since the none of the
ADAT digital inputs and outputs invert the data), what matters is what generation of ADAT
recorder was used when the tape was recorded. You can straighten it out again by using the
polarity (phase) switches on your console. It pays to listen to a track both ways. Some things
actually sound better in a mix when the polarity is inverted. That’s why they put those switches
on the console.
Throughput Delay (Latency)
There’s practically none – only 1 sample in each direction, total round trip of just under 21
microseconds at 48 kHz. This doesn’t mean that you’ll avoid the possible monitoring problems
discussed with the AIO-8 card. You still have to get in and out of the card through A/D and D/A
converters, so the actual delay you’ll get between input and monitor output depends almost
entirely on your outboard equipment. 1.5 or so milliseconds is pretty typical for most converters.
Where you’ll see a benefit to the very small throughput delay of the OPT-8 is when you bounce
tracks digitally. The bounced track will line up more closely with the originals.
Word Length
The OPT-8 is strictly a 24-bit device. It’s no problem if you’re transferring a 16-bit ADAT
recording or some tracks from a CD or DAT into the HDR24/96. If the Project is set up for 16-
bit, you’ll get the tracks transferred just as they were recorded. If the Project is set up for 24-bit
(for example if you want to add some new tracks to that 10 year old ADAT recording), they’ll
still go in just fine, with the lowest order bits all being zeros.
The OPT-8 provides no output dithering, so when digitally transferring a 24-bit project to a
recorder that uses a shorter word length (an ADAT, for example), the data will be truncated. This
isn’t the end of the world, but it usually sounds a little worse than if you had recorded at 16-bit
resolution and truncation wasn’t necessary. This is a decision that you should make when
planning the project. A truncated 16- or 20-bit backup copy is much better than no backup at all,
however, so don’t let this stop you from using the tools you have available for making backups.
PDI-8 AES/EBU Digital I/O
The PDI-8 is a general purpose digital I/O interface, which provides four pairs of channels in the
AES/EBU format. The PDI-8 is the only Mackie digital I/O card (at the time of this writing) that
supports 88.2/96 kHz sample rates as well as 44.1/48 kHz.
Inputs and Outputs
The PDI-8 has a single 25-pin D-subminiature connector, which incorporates both inputs and
outputs. Inputs and outputs are differential and balanced, in compliance with the AES3 standard.
HDR 24/96 210