Apple Logic Pro 7 (TDM Guide) - Manual (Page 15)

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About TDM
Logic Pro allows you to make use of the TDM functions
supported by ProTools HD Accel, HD, Mix, and 24/MIX
systems.
TDM stands for Time Division Multiplexing, the time-interlaced transmission of several
digital audio signals through a single data bus. This bus system is physically isolated
from the computer system bus, and runs between the individual TDM-capable PCI
boards. 256 (MIX) or 512 (with HD/HD Accel) digital audio channels, each with 24 bit
resolution, can be transmitted on the TDM bus. These signals form the signal paths
within a virtual mixer. These signal paths are necessary for the insertion of plug-ins,
which are calculated on the DSP card (DSP = Digital Signal Processor), and routed into
the individual channels, or are selected through auxiliary busses.
Note: You should only use hard drives mentioned on the compatibility list provided by
Digidesign, for recording.
Pro Tools HD systems increase the sample rates possible, the number of tracks and the
number of channels on the TDM II bus.
Note: It should be noted that the TDM channel count is sample rate dependent, so if a
rate of 88.2 or 96 kHz is used, the 512 channels available to a PT HD system will be
halved to 256. At a sample rate of 192 kHz, this will again be halved to 128.
Differences to Native Processing
Basically, the use of Logic with a TDM system is very similar to the use of Logic with the
native processing capabilities of your computer. Here is an overview of the main
differences between the two systems:
• In a TDM system, all audio processing is done by the DSP chips incorporated into the
TDM hardware. This means that the native Logic plug-ins cannot be run on the TDM
DSPs. TDM plug-ins, however, can be fully used and automated.