I received SN76489 chips so I updated my hardware VGM player with one of them and I almost had the pleasure to get it working on my first try (everything was ready from the code to the electronics) but I now have a very strange issue with the noise channel.
Before going any further, I've to say that I know very well I won't get a sound close to the MD/SMS because of the different shift register implementation. But all the documentation I read about this says that it ends up with a "slight" difference in the result from the noise channel.
My problem here is that all the three tone channels are working perfectly, but the noise channel is not. To be very precise, it sounds like a very low pitched rumble almost all the time (where it should be like a high "hiss" sound for hihats and so on).
My question is : is this the real difference between the VDP and a SN76489 (meaning, it _really_ doesn't sound the same at all) ?! Or am I just having a little issue I should be able to fix ?
Here are records I've made (using a song from Street of Rage) to explain a little more :
Audio files #1 and #2 come from a software VGM player I made (which features Maxim's PSG noise implementation BTW
![Smile :)](./images/smilies/icon_smile.gif)
Audio files #3 and #4 come from my hardware VGM player. You'll notice the global pitch is a little higher. That's because I'm waiting for a second adjustable clock generator (the YM actually has one but I tuned it up a little so it fits more nicely with the SN76489 which runs at 3.68 MHz instead of 3.57 MHz). #3 has all channels (YM2612 + SN76489), #4 has just SN76489. At the end of file #4, I stopped the VGM stream so the chip is "frozen" in its state so you can hear the really wrong noise it makes.
For a quick comparison, just listen to audiofiles #2 and #4 and you'll hear the three tone channels working but not the noise channel.
Audiofile #1
Audiofile #2
Audiofile #3
Audiofile #4
Hope someone will have any clue !
Thanks for reading.
Cheers,
sig