CPC464 designed background noise

[maschinist]

Hello

There is that interesting background thinking noise the cpc464 comes with and what makes the cpc somehow special.
An explanation was given in the magazine AmstradComputerUser02-1084.pdf on page 36 (attached). 

I still have questions:

* How is that implemented technically?
* can this be amplified a little more?
* Are there emulators adressing this "thinking" sound?

Thanks
RST

[Bryce]

Hi maschinist,
           still laughing at the "How is it implemented question"!! It's not "implemented" , it's a side-effect of the crap amplifier design, which is neither isolated nor screened.

Bryce.

[mr_lou]

It's not a fault. It's a feature

Good one.

[maschinist]

Alright, thank you for clearificaton.  I got it.

[Gryzor]

Heh, I remember reading that ACU reply... It's delivered in a quite serious manner so I bet lots of users fell for it back then

[Lazy Dude]

maybe its my imagination, but the audio line out is a lot cleaner than some later PCs and laptops, i never used the internal speaker

[maschinist]

could be emulated by sending upper addres + lower address bus + data bus to /dev/dsp? 
just a thougth...

[Devilmarkus]

Simple to emulate:


Emulating CPC 464 designed background noise - YouTube

[maschinist]

Wow - that is awesome.
This emulation sounds like on a real vintage machine. 
Thumbs up!

Maybe the only difference to the real cpc464 is maybe the 50 Hz.
When I switch on my >>GT 64<< my desk is vibrating @50...

[Devilmarkus]

To emulate it:
Just check the memory part in your emulator source...
Where your emulated CPC memory reads bytes (usually a code like this:

Code Select Expand


    public int readByte(int address) {
        int result = mem[readMap[address >> 13] + (address & 0x1fff)] & 0xff;     
        return result;
    }
)
Just send the read value with volume down to an audio device:
Use an Integer like bytenoise and feed it before you return the result:

Code Select Expand


    public int readByte(int address) {
        int result = mem[readMap[address >> 13] + (address & 0x1fff)] & 0xff;       
        bytenoise = (result & 0xff) >> 6;
        return result;
    }


[Devilmarkus]

I added this (lousy) emulation on JavaCPC Applet...
http://cpc.devilmarkus.de (All old-cpc games and demos will feature this now)

Numberpad + key: enable background noise
Numberpad - key: disable background noise

[Gryzor]

Heheh silliest, funniest thing in a long time