The Cyndustries List

My testing method isn't a problem.  The output impedance of the source 
doesn't matter for the measurements I did.  I adjusted to get 1.000 
volt, as measured at the 1V/oct input.  (Measured at the output pin of 
the op amp in my mixer, the voltage would be 1.010 volts, because of the 
1K/100K divider formed between the mixer output and the 1V/oct input on 
the ZO.)   Tracking two oscillators isn't the main point here.  It's the 
irregularity of the response of a single VCO over several octaves.  If 
something was amiss with my test method, it would have shown up on the 
MOTM-300 too.

-Richard

John Loffink wrote:

>Richard,
>
>For your testing, what is the output impedance of your Mixer-Comparator?
>Unless it is the range of ~100 ohm or less, it may cause some of the error
>you are seeing.
>
>An MOTM 820 VC Lag has a properly designed output for accurate 1V/oct
>tracking.  You may want to put your voltage source through that for your
>measurements.
>
>For any broad tracking between ZO and other VCOs, I am thinking you may need
>to use a soft sync function between them.  No matter how accurate the VCOs,
>there will be differences in beating through the audio range.  Because one
>VCO is used as a modulator, the beating may sound more prominent than two
>VCOS that are simply mixed in parallel.  
>
>John Loffink
>The Microtonal Synthesis Web Site
>http://www.microtonal-synthesis.com
>The Wavemakers Synthesizer Web Site
>http://www.wavemakers-synth.com
>
>
>  
>
>>-----Original Message-----
>>From: The_Cyndustries_List@yahoogroups.com
>>[mailto:The_Cyndustries_List@yahoogroups.com] On Behalf Of Richard
>>Brewster
>>Sent: Sunday, February 26, 2006 6:27 PM
>>To: The_Cyndustries_List@yahoogroups.com
>>Subject: Re: [The_Cyndustries_List] ZO 1V/Octave calibration
>>
>>Thanks, Cynthia.  I found the trimpot easily.
>>
>>I ended up with a setting close to the original factory setting. But I
>>was not able to fix a problem of the ZO tracking sharp in the lower
>>octaves of the high range. I started down this calibration road because
>>I noticed that the ZO and the MOTM-300 being used as the FM source in
>>the starter ZO patch were not tracking each other well.  The beats were
>>quite noticable.  I spent a couple of hours taking measurements, after
>>setting the 1V/oct trimpot.  Here's what I found.
>>
>>I measured with a digital voltmeter and a digital frequency counter.
>>For comparison I performed the same tests on the MOTM-300 VCO.  The
>>results were all obtained by the same method and instruments, using the
>>same power supply.  I created a 1V source by a mixer with bias (my own
>>mixer-comparator) and measured for 1V at the 1V/oct input jack.  For
>>each reading I dialed up a frequency, applied 1 volt and recorded the
>>new frequency, which ideally is double for the next octave.  For the ZO
>>I did this in all four combinations of High/Low Bias and High/Mid
>>range.  I only measured what I could dial up that started in the audio
>>range. Each number pair below represents the HZ value before and after,
>>so 30/60 means 30HZ/60HZ.
>>
>>Low Bias/Mid Range
>>30/60 - right on
>>60/119.8
>>
>>Low Bias/High Range
>>30/66
>>60/123.2
>>120/241.5
>>240/480 - right on
>>480/957
>>
>>High Bias/Low Range
>>30/60.2
>>60/120 - right on
>>120/239.7
>>240/478.4
>>
>>High Bias/High Range
>>30/66
>>60/124
>>120/243
>>240/482
>>480/960 - right on
>>960/1916
>>1920/3825
>>
>>MOTM-300
>>30/60 - right on
>>60/120 - right on
>>120/240 - right on
>>240/480 - right on
>>480/960 - right on
>>960/1918
>>1920/3834
>>
>>The ZO tracking isn't bad, but it isn't great either.  The ZO starts out
>>on the low end tracking more than one octave per volt (sharp), passes
>>the sweet spot and starts going flat gradually.  By contrast the
>>MOTM-300 tracks perfectly over about six octaves and then also start
>>going a little flat.  Now this flatness on the high end may be by
>>design, due to psycho-acoustic effects, I seem to recall. I'm not a
>>music VCO expert. But sharpness on the low end isn't good.
>>
>>For my ZO the tracking is accurate over at best about three octaves.
>>The lower octaves track better in the low range and the higher octaves
>>track better in the high range.  This was a useful finding.  Of course I
>>tested only my own ZO, so I can't say whether this is the general
>>character of a ZO or not.  Still, I would be interested to hear from
>>other ZO owners whether they are able to replicate my findings.
>>
>>-Richard Brewster
>>
>>http://www.pugix.com
>>
>>
>>
>>
>>
>>
>>    
>>
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