Hello and thank you for the posts
With regards to the OBD lead there are a number on the market, the choice is really which do you buy based on use and of course cost.
Do you have an OBD tool already in use utilizing the J2534 protocol via USB? (Not Bluetooth)
If so this may well function with the NVH software.
The lead I am using is the Mongoose Pro (optimized for Toyota) but has functioned with every vehicle I have connected to so far via the J2534 protocol.
Once connected , the NVH software requests Engine speed, Road speed and VIN. All of which are surrendered by the on board PCM and displayed in the NVH analysis screen.
The alternative method for engine speed input is via Channel D (4th Channel) of the scope as you have mentioned. This could be a pulsed signal relative to engine speed. You could therefore connect to the crank sensor and adjust the "pulse per rev" setting in the set-up wizard of the NVH software until you have the correct engine speed (Often 60 or 36 pulses per rev).
Here then, the raw speed signal is fed into the PC (via the scope) to the NVH software which displays and graphs the engine speed for view in the signal history chart. (No OBD link required)
Should you wish to obtain road speed, you would then need to enter transmission / differential ratios and Tyre size, then select "Calculate Road Speed" under the options menu.
When using the microphone you are correct, this will consume one channel of your scope only, using the included
Regarding the number of parameters available via the OBD, theoretically those covered by EOBD regulations should be accessible with minimal research / code cracking.
At present the NVH software only asks for engine speed, road speed and VIN.
In the future this potentially could be extended.
I hope this helps, take care........Steve