User guide

MS-DMT Guide v1.04

Released 05-30-2014

The technical read on all this is that the hardware is programmed with the sample rate at every

call to KsCreatePin:

http://msdn.microsoft.com/en-us/library/ff561652.aspx

Each exclusive mode stream results in a call to KsCreatePin.

A shared-mode stream will either:

1 .Result in a call to KsCreatePin (if there are no other shared-mode streams active)

2. Result in the audio engine mixing multiple streams and passing the mixed result down to the

already-created KS pin

The "default sample rate" exposed in the Sound control panel is what the audio engine passes to

KsCreatePin for shared-mode streams.

At present this software uses one channel at a 16 bit sample size and 48kHz raw sample rate

only and performs high quality sample conversion between 48kHz and the 9.6kHz sample rate

required by the modem. Additional raw sample rates of 96kHz and 192kHz and additional

sample sizes of 24 and 32 bits are planned for user selection so that the user can select the

maximum native sample rate their sound device supports without software resampling coming

into play and the best sample size. When the software provides greater sample size selections

the user will need to note their sound device dynamic range to make the best choice.

Many 24-bit cards only have a dynamic range (Signal-to-Noise Ratio) of about 100dB, which

actually corresponds to a resolution of only 17-bits. Whereas a 16-bit sample size theoretically

provides 96dB of dynamic range. In other words, the additional bits are used to digitize noise.

Thus using 24-bit cards at the currently coded 16-bit resolution in this case is better than using

24-bit resolution as there is no additional noise. Thus when 24-bit and higher resolution is

coded, it will be up to the user to determine what selection is best with their hardware.

NOTE: Under Windows 7 and likely later, the MS-DMT application must be the first and preferably the

only application running that uses the sound device. If the MS-DMT application is not first and the first