Not to sure what you mean by interface?
Interface = the way in which you connect your gear outside of your laptop, to your laptop. The VX Pocket's are examples of that interfaces. There are three primary interfaces you may use, generically speaking:
[1] mics > preamp > laptop interface (including ADC) > laptopIn this case, the ADC process takes place within the interface itself. I believe both the VX Pocket's support this capability. Ideally, however, we want the ADC to take place before the interface.
[2] mics > preamp > ADC > laptop interface > laptopHere, the analog-to-digital conversion takes place outside of the interface and laptop - exactly what we want to happen. I believe both VX Pocket's will receive a digital signal from the ADC and pass it into the laptop. If the external ADC does not include a USB output, then this type of interface is required.
[3] mics > preamp > ADC > laptop (using built-in interface)Alternatively, some ADC's may take advantage of the built-in interfaces in the laptop, the most common of which are USB or Firewire. For example, the Edirol UA-5 may output its digital signal via USB, in which case you don't need a VX Pocket.
and what goies into the decison to use a pre or not to use a pre..... thanks ton!!
Per the
Getting Started thread (if you haven't read it yet, please do), we generally require gain to amplify the signal level produced by the microphones. Preamps are one way of adding gain. If you don't use a preamp, you need an altnernative way of adding gain. The best alternative to a preamp for gain: line transformers. However, most preamps provide functions other than simply gain, mainly phantom power for the microphones. Line transformers do not. So while line transformers are less expensive for gain, you still need to purchase a phantom power source for the mics.