2600 VCA

Alan Brown
  • Alan Brown

    Alan Brown - 2009-03-07

    Nick, On my machine at least the VCA does not appear to be working as per manual.  I will send you a patch, which is VCO3 triang into VCF full on, VCF to VCA full on, VCA to mixer full on, everything else off. I believe I should be getting sound at the same level as I would if I closed the VCA to mixer off and opened the VCF to mixer full on. However I am getting nothing - I can only get sound out of the VCA if I feed a control signal to the VCA.



    • Nick Copeland

      Nick Copeland - 2009-03-07

      Hi Alan,

      This looks like it is a difference in the controls I implement since I agree that this should does not make a sound based on how the emulator works: The VCA has a number of inputs that control its gain, if no control input is give then the amplifier does not open, the output will be zero.

      What the 2600 does here is apply an 'initial volume' to the VCA to make it 'drone', some of their other synths such as the Odyssey do this. I use the Global Volume controller to control the gain of the final output signal, it does not have any to do with the VCA.

      There are some good arguments for the bristol behaviour:

         1. This is a polyphonic emulator, so a note is only playing whilst you have the key pressed. If there is any drone configured it does not work with polyphonic key assignments since it goes on and off with the MIDI events. A side effect of going on and off with midi events is that it introduces key clicking as the gain effectively goes from zero to unity immediately with key-on events.

         2. Since the VCA will give constant gain if you only apply an 'initial volume' then you can get most of the same results by not using the VCA - patch around it directly.

      I am not certain I want to get rid of the Global Volume. I could add in another control underneath it called 'Initial Volume'. If fact, I should add in another two controls:

      a. Global Volume stays but should not be saved in the memory, it is set for each session.
      b. Memory Volume is added and is the volume per the given memory for equalisation.
      c. Initial Volume is added and is the drone state of the VCA.

      Not sure what you think of that. Its a little outside of the specification of the ARP but polyphonic processing is also out of that specification so perhaps this is a reasonable set of parameters to apply. Something should be done since otherwise some capabilities would be hard to emulate (Envelope with non-zero floor for example).

      Kind regards, Nick

    • Nick Copeland

      Nick Copeland - 2009-03-07

      So Alan,

      After some consideration I went ahead with the 3 different volume parameters, there was too many good reasons to implement it this way - the next release will have parameters a, b and c from the previous entry. It should not affect existing memories and init.volume should give you droning as per the original.

      I will send you the two files if you want (same ones again) per email so you can try them out. Many thanks again for the report.

      Kind regards, Nick.

    • Alan Brown

      Alan Brown - 2009-03-10

      Nick, Thanks for the files, I have to admit, that until I installed them I struggled to understand what the first response you gave. However after installing the additional volume parameters make a bit more sense. I understand the global volume and the init volume, but what does the memory volume do? Is this something that you can save with each patch so that the relative volumes of each patch that is created can be set? I will experiment some more

      After a quick play the VCA seems to behave as I expect with the init volume. Sorry I haven't been able to respond sooner, but I haven't been able to play on my computer for a couple of days. Your responses put me to shame a bit. I'll look forward to progressing further in the manual


    • Nick Copeland

      Nick Copeland - 2009-03-11

      Hi Alan,

      You are quite right about memory volume and global volume: one is in the memory, the other just sits there. The actual volume of the output is the product of these two variables so each memory can be equalised to each other and the output of the synth can be equalised to other intruments you are playing.

      Kind regards,


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