how do I get the wavetable to run at 50Hz

[Dr_Nick]

I was trying to use the wavetable as described in the old v1 turorial (http://www.ucapps.de/howto_sid_wavetables_1.html), but I just can't quite get my head around the correct settings for clock speed and wavetable rate to achieve an 50Hz rate. 

Also, in the manual for the lead engine there is a divider of 3 mentioned for the clock, but I can't find a way to set that divider.

Plus I don't really understand the difference between the +/-xx and absolute xx values in the wavetable: I am trying to get a short 3 octave arpeggio using a wavetable, starting at position $00 and looping to $01. Parameter is 37 (Transpose OSC#1). The sequence 40 +18 -0c -0c works as expected, but +00 +18 -0c -0c does not. But why?

 

Regard, 

Dr. Nick

[TK.]

I don't remember all the details of this v1 firmware which has been developed more than 10 years ago, but from the source code it seems that the rate is multiplied by 2, and not 3 as you mentioned.

 

This is what I wrote in the documentation (-> http://www.ucapps.de/howto_sid_wavetables_1.html)

 

 

In order to reconstruate this waveform, first you have to select the same wavetable rate. Since MIDIbox SID clocks the sound engine much faster than a C64 (0.819 mS update cycle), the wavetable has to be slowed down. The wavetable update period can be calculated with following formula: period = 2 * (127-rate) * 0.819mS. In order to get a period of 20 mS, the appr. rate is 115

 

So: could you please try 115? The resulting rate will be 19.67 mS = 50.89 Hz, but I hope that you are happy with this setting anyhow.

 

 

 

Plus I don't really understand the difference between the +/-xx and absolute xx values in the wavetable: I am trying to get a short 3 octave arpeggio using a wavetable, starting at position $00 and looping to $01. Parameter is 37 (Transpose OSC#1). The sequence 40 +18 -0c -0c works as expected, but +00 +18 -0c -0c does not. But why?

 

because you only increment and decrement values, you never start with an absolute value. This won't work.

And therefore the first sequence (40 +18 -0c -0c) was better.

 

Do you know these tutorials?

-> http://www.ucapps.de/howto_sid_wavetables_1.html

-> http://www.ucapps.de/howto_sid_wavetables_2.html

-> http://www.ucapps.de/howto_sid_wavetables_3.html

 

Especially in the third page it's mentioned again, how to select ca. 50 Hz - so, probably you will find much more new informations there ;)

 

Best Regards, Thorsten.

[Dr_Nick]

Thank you for your fast reply!

Actually I'm running the latest v2 firmware, so after reading the old v1-tutorials mentioning a value of 115 I was trying to figure out the right combination of clock rate in bpm and speed value in the "wtc"-menu.

In the v2-manual for the lead engine there is a divider of 3 mentioned as an example in the sections describing arpeggiator and wavetable settings ("Spd (Speed): the wavetable speed derived from the global clock. If the global clock is synched to a MIDI clock master (slave mode), and the divider is 3, a speed value of 1 will step the wavetable on each 32th note. A value of 2 on each 16th note, a value of 8 on each beat."). Is the value for the divider anything you can or should change somewhere in the menus?

 

Regard,

Dr. Nick

[TK.]

Ok, now I know from where the confusion is coming from... ;-)

 

The special divider mentioned in the user manual doesn't exist anymore... I just have removed it from the documentation, and improved the examples.

 

For 50 Hz you want to step the WT or ARP each 20 mS.

At 124 BPM (= 5 mS per tick), you could achieve this by setting the speed to 4

 

Alternatively, you could clock the WT from an LFO with a constant frequency: go to the "Clk" trigger, and disable the connections for W1S, W2S, W3S, W4S

Then go to the L1P trigger (or whatever LFO you want to use) and enable the connections there.

 

Best Regards, Thorsten.