User guide

MS-DMT Guide v1.04

Released 05-30-2014

PC SOUND DEVICE SELECTION

All PC Sound Devices (a.k.a. Sound Cards) are not created equal and all operating systems do not

treat the same sound device equal. There are a number of important considerations when

selecting the sound device for use as the hardware modem portion (PC Sound Device Modem)

of this software solution.

This software requires an Audio Codec 97 (AC’97) compliant or better mono sound device with a

native sample rate capability of 48khz at a 16 bit sample size and at least 100-4,000hz flat

frequency response. Details are provided on sound device driver configuration in the next

section, which cover devices with greater raw maximum sample rate than 48kHz.

The dynamic range and frequency response of the average sound device is more than adequate

for the software modem needs, however sound device must provide:

 An accurate sample clock (less than 10ppm being best) on input and output

 Low sample clock thermal drift stability

 High Signal to Noise Ratio

 Total Harmonic Distortion + Noise

 Low deterministic phase jitter

Low deterministic phase jitter is a big issue in digital audio system related with timing variation

in variable clock position. If you have big/high jitter in your system (ADC or DAC), then the actual

result of the conversion process can be either too early or too late rather than ideal.