MACKIE HDR24/96 - Manual (Page 211)

HDR 24/96
At 44.1/48 kHz sample rates, each input and output carries a pair of channels. When operating at
high speed, the four pairs of channels become four single channels in the double wire (“double
wide”) format.
The output voltage between hot and cold is 5V peak-to-peak into 110 ohms, the standard
operating voltage for an AES/EBU inputs. If you want to connect a coaxial S/PDIF input or
output to the PDI-8, we recommend using a 75-to-110 ohm transformer to match both level and
impedance. A hard-wired “Pin 2 hot” XLR-to-RCA adapter may or may not work, depending on
the S/PDIF equipment.
Transformers we’ve tested are Canare BCJ-XJ-TRA or Neutrik NA-BFX for AES/EBU-to-
S/PDIF and Canare BCJ-XP-TRA or Neutrik NZ-BMX for S/PDIF-to-AES/EBU connection.
Those have BNC connectors on the 75 ohm side, so you’ll probably also need BNC-to-RCA
adapters.
Signal Polarity
Signal polarity is preserved when going in and out through the PDI-8
Throughput Delay (Latency)
Delay through the PDI-8 is 2 samples in each direction, about 42 microseconds at 48 kHz, 21
microseconds at 96 kHz. As with other digital I/O cards, the total delay time from microphone to
headphones is largely a function of the A/D and D/A converters.
Word Length
Input and output is 24-bit. The output is always a 24-bit word regardless of the word length
selected for the project. Input can be any word length up to 24 bits. If the project is at 16-bit
resolution, the output will be 24 bits, with zeros in the eight low order bits.
Channel Status Bits
Consumer (S/PDIF) and professional (AES/EBU) devices make different use of the “non-audio”
data bits in the digital audio frame. The Setup menu for the PDI-8 allows you to choose between
those two formats for each channel pair. The PDI-8 will accept either format with either setting,
but some devices (DAT or stand-alone CD recorders, but rarely computer sound cards) are fussy
about this. The usual symptom is an indication that the source is copy-prohibited. If your unit
refuses to record the output of the PDI-8, try changing this setting. The audio data is the same for
either format, so don’t feel like you’re compromising professional sound quality by selecting the
Consumer status bit format.
Sample Rate Conversion
The PDI-8 can be set up to convert the sample rate of the incoming digital signal. This is useful
if you’re working on a project at 48 kHz sample rate and someone, for example, brings in a CD
from which they want to create a drum loop. If your CD player has an AES/EBU or coaxial
S/PDIF output, you can connect it to a pair of inputs on your PDI-8 card and, from the Digital I/O
Setup menu, select Convert Sample Rate on those inputs. Regardless of the incoming sample
rate, the recorded sample rate will be the sample rate of the project. This is also useful if you
have multiple digital sources with no way to synchronize their word clocks.
When sample rate conversion is enabled, the lower four bits of audio data get lost in the process,
so even though a full 24-bit word is being recorded, only the first 20 bits are significant. Of
course this won’t matter at all if you’re sample-rate-converting from a CD or DAT, since they’re
only 16-bit sources. In reality, even if you have a 24-bit source that you need to convert to the
project’s sample rate, it won’t make an audible difference as few A/D converters are capable of
accurate conversion down at that level. But we just thought you’d want to know.
Technical Reference 211