Newbie question - how to start sine at zero crossing?
 

Hi,
I'd like to generate a 60 Hz sine wave using the Virus Ti and Virus control. In particular I'd like to sine wave to start at zero each time a note on midi command is sent, i.e. the sine wave would always start at the same phase angle, i.e. zero. Is this possible? If so how would I go about it?

I realize I could just generate a sine wave and then cut it at the zero crossing using a wave editor, but I'd like to do this with the TI.

I've tried fooling with the "Init Phase" control; doesn't seem to let me do this.

If anyone could give me a hand with this problem I'd really appreciate it.

Many thanks,
T

just as a matter of interest, what are you trying to achieve by doing this

If you look at this:

http://en.wikipedia.org/wiki/Piano_key_frequencies

You'll see that none of the standard notes are exactly 60Hz. The nearest is key Bb1 (A#1) at 58.2705Hz. You would have to tune the frequencies in some way to hit 60Hz, either via Master Tune (to tune the whole keyboard up or down), or fine-detuning in cents (to tune the oscillator up or down). You might not even be able to get 60Hz exactly. Use Oscillator2 (Osc1 doesn't have fine-detune available).

You'd need some sort of external frequency analyser to check the tone.

Regards Phase..

A phase-init value of 0 turns phase off. The oscillators will be free-running (random).

A phase-init of 1 starts Oscillator1 at 0º. This is what you need. If you want to start halfway at 180º (the other zero cross point in the waveform), then you'd need phase-init at a value of 64 or 65 or similar. A phase-init value of 127 is nearly 0º again.

Hi Timo,
thanks for you help!

Background: I was trying to build this patch by starting off with the "init" patch using virus control only.

Originally I did try to set the phase-init parameter to one but nothing happened; the oscillators still behaved as if they were free running.

Then I tried to route some modulations with the matrix - nothing happened
Tried to instantiate the soft-knobs - nothing happened.

After 3 hours of fooling around, I then loaded the "tutorial 1" patch in slot #1. Then I loaded "init" in slot 2. Now suddenly everything worked like it should - setting phase-init to 1 started all the waveforms at zero. I suspect that loading "tutorial 1" reset some communication parameters to allow the other settings to work.

Also: I'm not that interested in obtaining a 60 Hz note. I'm doing this to sound design a bass kick drum. Hence I'll set the pitch of the note to something harmonious with the root note of whatever track section I'm working with; eg if the track starts off in C I'll set it to a low C.

I mentioned 60Hz partly to avoid a long explanation that wasn't really related to the problem and partly because mixing 60Hz waves into kicks is something that I know others have done.

What I'm really trying to do is produce a sine wave that starts off at low C and then is pitch modulated from it's original note down one octave. I'll use this as the "tail" end of a kick drum. For the front end or attack I'll cut that from a sample. If I remember correctly infected mushroom uses this technique for some of their kicks. I've got a protocol to do this in Soundforge but I'm trying to program it in the Virus TI in order to get to know how the synth works. I've done very little synth programming and am learning the basics.

I said the problem was partly solved because even though the wave starts at zero I still don't get a precise sine waveform with the ADSR attack set at zero. The amplitude of the first half of the initial sine wave is too low and the second half is too high; then all the peaks and valleys are equal thereafter.

Thanks again,
T.

PS I have no idea about the user customizable wavetables, etc. Sorry!

A little-known feature of Phase Init is that it works differently for Osc1 than it does for Osc2.

For Osc1, values 1-127 are all the same (i.e. the parameter is effectively restricted to 'on' and 'off'), but for Osc2 they do actually represent a different phase.

The tutorial patch would have been made using only Osc1.

So, if you want to set a specific start point, then Oscillator 2 is the one to use.

..and you know to turn off Punch Intensity when you're trying to achieve pure waveforms, right?

Hi Ben,
thank you very much - your comments are very helpful. I did turn off Punch Intensity on Virus control but I'm not sure that the parameter change was transferred to the virus TI (see below).

It turns out that I'm having a major communication issue between virus control and the Virus TI desktop. When I try to update certain parameters on the TI using virus control, the update doesn't always transfer to the the TI. The parameter changes in Virus control but not in TI. If I go and twiddle knobs on the TI, the corresponding parameter in virus control changes. This only happens for some of the parameters, for example I see this behavior with the mod matrix the oscillator page seems to work normally.

I'm using OS 3.04 cubase 5, xpsp3 and a core i7 unit. All my other usb devices seem to work fine. I'm using a dedicated usb card for the virus TI. So far I've tried uninstalling the driver, re-installing it and switching the USB cable to another port on the card.

Any ideas re: what I could try next?

many thanks,
T