Improve pulse channel audio

[DaveTCode]

Running SNDTEST2.NES with the following configuration:

(that is, full volume, timer = 255). So pulse = fCPU/(16*(t+1)) suggests that should have frequency ~440Hz.

Attaching audacity to the loopback device for my speakers and playing that gets me:

Put through plot spectrum gives:

Running exactly the same process on Mesen gives the waveform:

and spectrum