I've finally gotten around to running some tests to try to determine how to best calibrate my MOTU M4 for interfacing with my eurorack system. Within drambo I programmed a melodic MIDI sequence using 1-octave intervals (C2-C3, and C2-C1), and I patched Drambo so that the MIDI sequence would be converted to CV and then output to my audio interface. Then I used my oscilloscope to measure the voltage at the output of my MOTU interface (ie. measuring the voltage if of different pitches and intervals). I found that C2 == 0V. Since eurorack modules tend to use 1V/oct as their standard tuning, I wanted to scale the CV generated by MIDI in drambo so to align with the eurorack standard. I found that by scaling by a factor of about 1.5325, I was able to achieve 1V/oct.
1.5325 is a very specific and unusual, almost arbitrary-seeming value. I'm not sure why Drambo would have been designed that way -- it's a very odd choice. I'm not sure if I made a mistake during my measurement and calibration process. Or perhaps every audio interface would require its own specific and particular scaling factor to convert Drambo's CV units to actual real-world voltage units?
How are other eurorack users handling this? I read in an old thread from many years ago that at one point, it was theorized that scaling by 0.8 would convert from Drambo's tuning system to Eurorack's 1V/oct tuning system -- but that old comment didn't describe how that conclusion was reached or what sort of signals need to be scaled by 0.8. In any case I'm observing very different results now, which is confusing to me.
EDIT: I should add I was running Drambo within AUM during these tests. But (in theory?) I wouldn't expect it to make any difference, since all other channels in AUM were muted/bypassed, and this channel was set to unity gain.
Unfortunately, there is no single standard describing what audio signal should produce what output voltage, for several reasons:
Audio interfaces are not designed for CV (DC) output in the first place.
If they happen to support it, calibration is up to you.
The idea of CV calibration is to find the precise values to obtain the correct pitches over many octaves.
Being able to use "odd numbers" is the idea of calibration, otherwise calibration wouldn't be necessary.
By the way, a classic multimeter will give you much more precise CV voltage readings than an oscilloscope.
Drambo should not care about absolute output levels because they're up to the audio interface's design.
Drambo's pitch signal is designed for working with Drambo modules and the common -1..1 range of internal values plus the 0.125 per octave scaling factor does make sense internally.
Don't forget that what you're doing here is an unsupported hack that happens to work well enough after some tweaking. Changing levels in your output chain at any point, be it the volume knob or internal mixer settings of the audio interface, will destroy the calibration again.
The "official" way to convert note pitches to CV would be a MIDI to CV converter. Much less hassle and potentially more CV outputs.
How are other eurorack users handling this? I read in an old thread from many years ago that at one point, it was theorized that scaling by 0.8 would convert from Drambo's tuning system to Eurorack's 1V/oct tuning system -- but that old comment didn't describe how that conclusion was reached or what sort of signals need to be scaled by 0.8. In any case I'm observing very different results now, which is confusing to me.
The reason is the interface itself. Different DC coupled audio interfaces will require different scaling (and potentially offset) values. The value 0.8 you mentioned sounds like a value to use for a specific CV interface from the company Expert Sleepers.
Expect live streaming, tech talk and dRambo shows.
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My music room is being relocated in to the new venue by the end of next week or by the beginning of the week after allowing for time because I also have to prepare for my gig with my live band mid May which is only around the corner.
a maximum voltage of 8 volts or a little bit more which can give you a bit of leeway
when calubrating 1v/oct from dRambo.
Can you explain what you mean by this? 8 volts where? Do you mean choosing a DC-coupled interface capable of outputting up to 8Vp-p? Or capable of outputting +/-8V? Or do you mean perform some sort of calibration involving 8V? How do you perform the calibration?
I would suggest not using the external cv module but going directly to the audio output
that you're using to send out CV signals and using the Scale Offset module to scale and offset the cv signal.
What do you mean by "going directly to the audio output"? I only just started using a multichannel audio interface (MOTU M4) within the past couple weeks, and I'm still learning my way around it. But I've found it not at all intuitive to understand how to control whether a physical output coming from drambo is mono or stereo. I've actually been emailing back and forth with MOTU support for days trying to better understand what's going on with mono/stereo signals on the iPad.
Could you please explain how to map the output from a Drambo track to the physical outputs of a USB audio interface? Especially when dealing with a combination of tracks where some are meant to be mono and some are meant to be stereo.
Comments
I've finally gotten around to running some tests to try to determine how to best calibrate my MOTU M4 for interfacing with my eurorack system. Within drambo I programmed a melodic MIDI sequence using 1-octave intervals (C2-C3, and C2-C1), and I patched Drambo so that the MIDI sequence would be converted to CV and then output to my audio interface. Then I used my oscilloscope to measure the voltage at the output of my MOTU interface (ie. measuring the voltage if of different pitches and intervals). I found that C2 == 0V. Since eurorack modules tend to use 1V/oct as their standard tuning, I wanted to scale the CV generated by MIDI in drambo so to align with the eurorack standard. I found that by scaling by a factor of about 1.5325, I was able to achieve 1V/oct.
1.5325 is a very specific and unusual, almost arbitrary-seeming value. I'm not sure why Drambo would have been designed that way -- it's a very odd choice. I'm not sure if I made a mistake during my measurement and calibration process. Or perhaps every audio interface would require its own specific and particular scaling factor to convert Drambo's CV units to actual real-world voltage units?
How are other eurorack users handling this? I read in an old thread from many years ago that at one point, it was theorized that scaling by 0.8 would convert from Drambo's tuning system to Eurorack's 1V/oct tuning system -- but that old comment didn't describe how that conclusion was reached or what sort of signals need to be scaled by 0.8. In any case I'm observing very different results now, which is confusing to me.
EDIT: I should add I was running Drambo within AUM during these tests. But (in theory?) I wouldn't expect it to make any difference, since all other channels in AUM were muted/bypassed, and this channel was set to unity gain.
Unfortunately, there is no single standard describing what audio signal should produce what output voltage, for several reasons:
How are other eurorack users handling this? I read in an old thread from many years ago that at one point, it was theorized that scaling by 0.8 would convert from Drambo's tuning system to Eurorack's 1V/oct tuning system -- but that old comment didn't describe how that conclusion was reached or what sort of signals need to be scaled by 0.8. In any case I'm observing very different results now, which is confusing to me.
The reason is the interface itself. Different DC coupled audio interfaces will require different scaling (and potentially offset) values. The value 0.8 you mentioned sounds like a value to use for a specific CV interface from the company Expert Sleepers.
See also:
https://forum.beepstreet.com/discussion/401/how-to-scale-drumbos-internal-voltage-to-eurorack
@aaa @rs2000
I'm in agreement with the both of you.
I started modular via dRambo and though dRambo's way of determine 1v/oct
works perfectly within dRambo it doesnt translate precisely into the real world
when using audio interfaces even when using an Expert Sleepers ES3.
My advice is to use a multimeter like @rs2000 suggested and create
a maximum voltage of 8 volts or a little bit more which can give you a bit of leeway
when calubrating 1v/oct from dRambo.
I would suggest not using the external cv module but going directly to the audio output
that you're using to send out CV signals and using the Scale Offset module to scale and offset the cv signal.
The other thing to bear in mind is that you will have to calibrate quite often when using external modular stuff.
Not because of the audio interface, because the external modules will drfit.
I designed a precison adder so that I can get the notes pitch perfect
however you can do rough calibration using just octaves and a tuner.
By the way part of the reason theres been tumbleweed is because I'm creating an Artist hub here in London, UK.
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My apologies if you don't use Facebook.
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Quoting @gravitas:
a maximum voltage of 8 volts or a little bit more which can give you a bit of leeway
when calubrating 1v/oct from dRambo.
Can you explain what you mean by this? 8 volts where? Do you mean choosing a DC-coupled interface capable of outputting up to 8Vp-p? Or capable of outputting +/-8V? Or do you mean perform some sort of calibration involving 8V? How do you perform the calibration?
Quoting @gravitas:
I would suggest not using the external cv module but going directly to the audio output
that you're using to send out CV signals and using the Scale Offset module to scale and offset the cv signal.
What do you mean by "going directly to the audio output"? I only just started using a multichannel audio interface (MOTU M4) within the past couple weeks, and I'm still learning my way around it. But I've found it not at all intuitive to understand how to control whether a physical output coming from drambo is mono or stereo. I've actually been emailing back and forth with MOTU support for days trying to better understand what's going on with mono/stereo signals on the iPad.
Could you please explain how to map the output from a Drambo track to the physical outputs of a USB audio interface? Especially when dealing with a combination of tracks where some are meant to be mono and some are meant to be stereo.
@aaa
There will be video about how to calibrate 1v/oct in a future video once my Patreon becomes active.
@lala has a Motu M4 I do believe so he maybe able to tell you how to configure your routing.