Apple Soundtrack Pro 3 - Manual (Page 517)

TDIF Connectors
Tascam Digital Interface (TDIF) is a signal format for transferring digital audio between
Tascam digital multitrack recorders or digital mixers. Connections are made via a 25-pin
D-subminiature connector and data is carried on shielded cable. Eight channels are
supported at sample rates of 44.1 and 48 kHz using 24 bits per sample. Higher sample
rates are available by pairing channels. The TDIF standard is currently one of two major
formats (the other being ADAT optical) widely used in professional products for digital
transfer of more than two tracks of audio simultaneously using only one cable.
TDIF connector
About Microphone, Instrument, and Line Level
Audio equipment can output line level at –10 dBV (consumer level), +4 dBm/dBu
(professional level), or microphone level, which is around 50 or 60 dB less than line level.
When you use a microphone, the level is very low, requiring a preamplifier to raise the
signal to line level before it can be recorded or processed. Most audio mixers, cameras,
and professional portable recording devices have built-in preamplifiers.
Instrument level is between microphone and line level, around –20 dBV or so. Guitars
and keyboards usually output at instrument level.
Signal Differences Between Pro and Consumer Equipment
Professional audio equipment typically uses higher voltage levels than consumer
equipment, and it also measures audio on a different scale.
• Professional analog devices measure audio using dBu (or dBm in older equipment).
0 dB on the audio meter is usually set to +4 dBu, which means optimal levels are 4 dB
greater than 0 dBu (.775 V), or 1.23 V.
• Consumer audio equipment measures audio using dBV. The optimal recording level
on a consumer device is –10 dBV, which means the levels are 10 dB less than 0 dBV
(1 V), or 0.316 V.
Therefore, the difference between an optimal professional level (+4 dBu) and consumer
level (–10 dBV) is not 14 dB, because they are referencing different signals. This is not
necessarily a problem, but you need to be aware of these level differences when
connecting consumer and professional audio equipment together.
517 Appendix C Working with Professional Video and Audio Equipment