Sound command vs pwmout

[ccdubs]

Hi,

I have been using the sound command to generate a tone at 1kHz to drive a speaker via an amp. The command is: sound 3, (116 ,250).

If you refer to my previous post yesterday I now want to try and get a 1kHz continuous tone so have used the pwmout command with a de-clocked processor at 1MHz. The command is: pwmout 3 , 249,500.

When I compare the result between the two the sounds are definitely at different pitch. I have proved to myself that the clock is running at 1MHz by writing a quick timer in my test code.

Can anyone verify that the inputs I am using in the sound command are correct? Without a scope it is difficult for me to determine what the frequencies are.

The note value of 116 was obtained from this post: http://www.picaxeforum.co.uk/showthread.php?t=7634&highlight=sound+frequency

Many thanks.

 

[eclectic]

Calibfreq?

ccdubs.
I've just tried this, using an un-calibrated 'scope and three different Picaxe chips.

Sound 1,(116,250) = ~997 Hz (One sample 08M)

Then, I tried
poke $8F,%01000000 : pause 10
pwmout 2 , 249,500 ' 08M ( pwmout 3 , 249,500 ' 18X)
stop

Results.
08M (1) = ~ 994 Hz
08M (2) = ~1010 Hz
18X = ~993 Hz

All four results are within 1% of nominal.
But, the differences are audible.

One possibility is to look at Manual 2, page 31 “calibfreq”
and then, very carefully, try it with your particular chip.

e.

 

[ccdubs]

Thanks for the assistance.

I have decided to use the pwmout command all throughout my code as I couldn't get the frequency close enough to what I want with the coarse options available.

I will have to live with freq "drift" between different chips.

 

[eclectic]

Ccdubs.

You might want to have a play with this.
I got the idea from
http://www.picaxeforum.co.uk/showthread.php?t=5872&highlight=jeremy+pwm*+poke

It's to run the PWMout at ¼ speed, but leaves the rest of the program at 4MHz.

#picaxe 18x

pwmout 3,244,500 ' Adjust as required
pause 2000
main:
Sound 1,(116,200) 

peek $12,b1 'read value of timer

b2 = b1 + 1 'add 1
poke $12, b2 'poke new value for 1/4 

noise:
sound 1,(116,255)
pause 1000
goto noise

e.