The Analog to Digital Converter

The CPC booster gives you the ability to make 8bit samples on the CPC. Ofcourse, there were some samplers in the past for the CPC, like the Music Machine, but this time it’s easier than ever! The sampler can be used only through assembly because in Basic the sampling rate is worse than an 1 bit sample!


ADDRESS:&FF0F IN/OUT ADC SAMPLING FREQUENCY
With this address, we can select the sampling rate. We don’t have to make complicated routines on the CPC, the baud rate can be set directly on the CPC booster, so we just make a simple IN to get the data and all the timing is done automatically. There are 8 possible values to select frequency, value 0 and 1 are the same:

VALUE DIVISION FACTOR SAMPLING FREQUENCY
0 2 5529 KHz
1 2 5529 KHz
2 4 2764 KHz
3 8 1382 KHz
4 16 691 KHz
5 32 345 KHz
6 64 172 KHz
7 128 86 KHz
As you understand, if the frequency is high, you have good quality but it takes a lot of memory and you can’t make long samples. In the worst quality, 86 KHz, you can create around 14 sec long sample, which takes 64 KB.

ASSEMBLY: LD A,3 ;Select 1382 KHz sampling freq.
LD BC,&FF0F
OUT(C),A
ADDRESS:&FF10 IN/OUT ADC CHANNEL SELECTION
With this address you select from which channel you will get the data. There are two channels, so we have the possibility to make stereo samples, or to record a stereo sample from a music CD and turn it into mono. To select channel 1, we send the value 0, to select channel 2 we send value 1. Any value between 2 and 255 selects channel 1 again (I’ve just noticed that!).

ASSEMBLY: LD A,0 ;Select channel 1
LD BC,&FF10
OUT(C),A
ADDRESS:&FF11 IN READ ADC VALUE
To read the data from the A/D convertor, we make an IN from this address. Could it be simplier? Here’s a routine which stores a sample with max width 10KB

LD HL,16384 ;Address to store the sample
LD DE,10000 ;Byte counter (10KB long sample)
LD BC,&FF11 ;Address for reading data
SAMPLE: IN A,(C) ;Read byte from the convertor
LD(HL),A ;Store byte in the address that HL points
INC HL ;Increase sample address to store next byte
DEC DE ;Decrease counter
LD A,D
OR E
JR NZ,SAMPLE ;Check if sample is 10KB long.
During the recording of a sample, you can adjust the incoming record volume with the potensiometer located on the top of the CPC booster. Use a screwdriver and adjust it till you get a clear sound. A way to do this adjustment is to make an in with &FF11 and send the value directly to the PWM.

Maintenant, je reste septique devant cette histoire de longueur, car la surface de contact de la masse est telle que tu devrais au moins avoir le son en mono.

En même temps pourquoi tu t'emmerdes avec ca au lieu de passer par ton PC pour faire ton sample ? Sampler sur CPC c'est une belle connerie, tu ne peux pas retoucher ton sample... Tout faire sur CPC ca a des limites.

Sampler sur CPC c'est une belle connerie, tu ne peux pas retoucher ton sample...

Tout faire sur CPC ca a des limites.