[sdiy] VCA signal analysis

Rutger Vlek rutgervlek at gmail.com
Sat Jan 11 12:11:04 CET 2014


Hi Terry,

Visual Analyzer looks good! As an alternative, I found Right Mark Audio Analyser through google http://audio.rightmark.org/products/rmaa.shtml.

Combined with my MOTU 828mk3 this is probably sufficient for the measurements I need to do, except... the output range of the MOTU is limited to about -4 to +4 volts, while I'd prefer to test the full range of 10V p.p. (-5 to +5 volts) common in modular synths (I'd also like to measure headroom to the point of 1% distortion). I could design a step-up and step-down opamp circuit to expand the range, but then I'd be measuring characteristics of that circuit too.... Has anyone run into similar problems?

Rutger


On 10 dec 2013, at 09:37, thx1138 wrote:

> Hi all,
> 
> Visual Analyzer is Free and is quite a good tool from Sillanumsoft on web.
> 
> I use it with my PC Laptop and M-Audio box.
> 
> It seems to work fine from my MacBook Pro under Fusion v. 6 and Win 7.
> 
> I also have an Audio Precision , but it is a bear to drag around for mobile projects.
> 
> best regards,
> 
> Terry p.s. I am in Erfurt Germany all week Damien.
> 
> Tchuss!
> On 12/9/2013 5:52 AM, Neil Johnson wrote:
>> Hi,
>> 
>> cheater00 wrote:
>>> [HP8903B]...and with 70 dB dynamic range perfect for testing the fidelity of
>>> transatlantic phone lines :-)
>> A rough hand-wavey estimate: at the top end the maximum input is 300V,
>> at the bottom end the residual noise and distortion (20Hz - 20kHz,
>> 80kHz BW) is 15uV (all datasheet numbers - I haven't had mine
>> calibrated yet so I can't give you cal.cert numbers), giving a dynamic
>> range of about 146dB.
>> 
>> For my purposes (messing around with old mixers and old analogue
>> synths, and designing synth modules) it's good enough.  If you want
>> more than that then you really need to step up to an AP.  I think Paul
>> Schreiber has (or had) one.
>> 
>> A notch filter also allows you to spend your limited sensitivity and
>> resolution on exploring distortion artefacts.  You can pump a healthy
>> signal into your circuit (VCA, filter, telephone line, etc), notch out
>> the fundamental, and then turn the gain up so you can see the all the
>> annoying harmonics from the distortion mechanisms in the circuit.
>> 
>> Neil
>> --
>> http://www.njohnson.co.uk
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>> 
> 
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