Digital audio boosting examples

[pixel]

I hear absolutely no difference with audio leak emulation turned on on Linux' VICE.

[Mike]

@pixel: PM sent

[Mike]

Eslapion, would you be so kind to cross-check my sawtooth example with your equipment?

* With just line 5 commented out you should get a "normal" sawtooth at ~1 kHz. *)

* With both lines 5 and 6 active, you should get a boosted sawtooth (i.e. with higher amplitude) but no clipping. However there's a 50% chance, that the boost voices aren't perfectly aligned, producing small distortions visible in the sawtooth slope.

* With line 6 commented out (i.e. just booster with silent sample at volume 15), are the spikes at 8 kHz visible over the bus noise? Again, they only appear with a 50% chance, so you might have to restart the program several times.


*) Edit: 1004 Hz with PAL, 926.4 Hz with NTSC.

[eslapion]

@mike
No Problem. please send a PRG file I can put on a 1581 floppy to eslapion@videotron.ca

I just looked at the schematic of the early VIC as shown in the VIC-20 Programmer's reference guide and you're right, an open-collector output is impossible. However, the current buffer with NPN transistor does act as a pull-down resistor of 47kOhms (470 Ohms through the base of a 2SC1815 with hfe near 100).

Is it possible then the audio output would be open emitter?

[Mike]

@eslapion: PM sent

[eslapion]

Data received! I must sleep - will try to inform you on the results tomorrow.

[eslapion]

Aargh!

I haven't used my 1581 drive in weeks and only now do I discover it was too dirty to read/write properly.

Had to dissasemble/clean heads/reassemble it. This will have to wait another day...

[eslapion]

my 1581 does have serious technical issues

Sorry to let you down guys

[eslapion]

I wanted to replace the drive inside my 1581 with a PC drive but it turns out my last "NOS" 3.5" drive does not have the DS0/DS1 jumper that would permit modding it for Amiga/1581 compatibility.

I just found a replacement internal Amiga 500 internal floppy drive and ordered it from a seller on Amibay. It's coming...

[groepaz]

If you switch on "VIC Audio leak" in VICE you get audio output very much comparable to the original hardware, including bus noise (noticible changing hissing upon different CPU activities) and a 50/60 Hz hum from the video circuitry

i take that as a compliment - because in reality it isnt anything like that =) its a big fake, and does hardly "emulate" anything. there is some random noise in 50/60Hz range, plus some additional noise which is AM modulated at 15khz by the average luminance of the current rasterline. no relation to "bus noise" in any way (that would be pretty hard to do in VICE). works reasonably well though, apparently )