MACKIE HDR24/96 - Manual (Page 208)

HDR 24/96
Signal Polarity
The polarity of the signal is preserved through the card. A positive-going input signal will be
recorded on disk as a positive-going waveform, and playback will be positive-going. This means
that if your cables are wired correctly, you need not worry about the recorder inverting the
polarity of your audio signal.
Throughput Delay (Latency)
Unlike pure analog hardware, everything digital requires some time for processing of an input to
occur before something comes out an output. The throughput delay through the AIO-8 card – the
time delay between input and monitor output in the Input Monitor mode (which passes through
both the analog-to-digital and digital-to-analog converters on the card) – is around 1.33
milliseconds at 48 kHz sample rate. That equates to 64 samples, 32 for A/D conversion and 32
for D/A conversion.
This isn’t enough time delay to throw off a musician playing to a recorded track or monitoring a
live mix in headphones, however, if the headphone level is close to the acoustic level at the
player’s ear, comb filtering can occur at around 755 Hz and multiples thereof. Where this is most
likely to occur is when a vocalist is hearing his voice in the headphone monitor mix at about the
same level as it’s getting to his eardrum through his throat. The length of the singer’s own
plumbing (another thing you can’t control) will also add to the monitoring delay, but the bottom
line is that this is a situation which may cause the singer’s voice to sound funny to him (and he
alone) in his headphones even though it sounds fine to you in the control room.
This is typical of any digital system, but since the HDR24/96 may be your first digital recorder,
we thought we’d explain it. The solution is to create a headphone mix for the singer, which uses
the mic preamp output rather than the recorder’s output for his voice. This is a piece of cake
when using an analog console, but not so simple when connecting a mic preamp directly to the
recorder.
Patchbays
The AIO-8 is the only Mackie I/O card that lets you connect signals on a channel-by-channel
basis rather than in groups of eight. It offers the most flexibility in signal routing, but to take full
advantage of this flexibility, we strongly recommend the use of a patchbay, at least for the
recorder inputs. This will allow you to use the shortest signal path possible (least amount of
electronics between the microphone or other source and the recorder) and easily record
successive tracks with the same microphone and preamp setup.
Connector Pin-out
The D-sub connectors used on the AIO-8 follow the same wiring convention as similar
connectors on TASCAM and Fostex equipment, so there are commercial, pre-made cable
assemblies available that mate with the DIO-8 connectors and provide various types of
connectors on the far end. If you want to roll your own, here’s the pin-out for the connectors:
If the table (following) doesn’t seem to make any sense, look at the connector. You’ll see that the
connections for each channel form a triangle of pins. Ground is the cable shield, Hot is normally
connected to Pin 2 of an XLR connector or the Tip of a TRS plug. Cold is normally connected to
Pin 3 of an XLR connector or Ring of a TRS plug. Ground is the cable shield, normally
connected to Pin 1 on an XLR or the Sleeve of a TRS plug.
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