There are actually two signals used in a DVS system.
One is a constant signal that identifies pitch and what most people think of in terms of the frequency.
Most all DVS use a signal between 1Khz and 3Khz, with the most common being 1.2KHz or 1.3KHz.
In most cases, the signal difference is a matter of semantics and diminishing returns as the signal just needs to provide an accurate signal back to the software to determine playback speed.
At 1KHz, an 8% change is 1080hz, and at 3KHz 8% up is 3240Hz. It provides a small increase in granularity, but that difference isn't noticeable by anyone that I know of. It's more likely going to show problems in system latency or other areas before they'll notice any difference in the frequency of the timecode.
More info:
http://en.wikipedia.org/wiki/Vinyl_emulation_softwareAnd here's a document written by Chad Carrier explaining how a DVS works. He was the product manager for Torq and now works for Native Instruments, but let's not hold that against him - the document is still pretty good.
http://www.mspinky.com/Some_Technical_Info_on_VInyl.pdf
read the manual for basic info on t c 
