Audio frequency range measurements, what hardware to choose ?

[Mark Masterson]

Hello guys.

My goal is to be able to analyze audio amplifiers, basically output power vs. THD, frequency range vs. attenuation, and output impedance (damping factor)
Was looking at many different measurement systems, and just can't understand, WHY they are soooo expensive ?

Used Keithley 2015THD for around 600$
Picoscope 4262 around 1000$
Used AP starts over 1500$
LinearX, Audiomatica and few others over 4000$
Not to mention Klippel for 6000$ for the hardware and another thousands of $ for different software modules.

And my question is: does it really have to be so expensive ? Even Arduino with 24bit ADC could measure it properly, em I correct ?
Is there any way for example to "tell" the Picoscope's software (since it's freeware) that for the soundcard that I have plugged in is "in fact" the required hardware i.e. 4262 ? In such way I could obtain all measurements needed with external sound card ?
I've got Mackie Onyx 400F which is much much more advanced than this dodgy 4262 hardware and I'm sure it is all I need...

Any tips will be much appreciated !

kind regards
mark

[commongrounder]

In my opinion, the main reason for the expense of these pieces of test equipment is to produce a useful measurement, the residual distortion and noise of the complete system must be at least an order of magnitude, or better, in specification, than any potential device under test.  At least in theory, these days, 24-bit digital devices can reach very low noise and distortion residuals, but in practice, achieving those levels requires some very sophisticated analog circuit design.   There are a couple of audio test units that are based on USB interfaces optimized for testing purposes, like the Quantasylum QA400 for around $200.00.  But these are not an order of magnitude better than the best analog audio gear out there.  If you want to check power output of amps at a certain distortion, then this kind of interface might work.

I am not familiar with interfacing with Arduino and others.  I'm sure other folks will chime in on this subject.

[AndyC_772]

Quite right - a 24 bit ADC is a relatively inexpensive, off the shelf component. An analogue interface, power supply, clocking and data acquisition circuit capable of actually extracting 24 bit performance from such a device is a whole different ball game, and is an extremely high precision piece of equipment.

As with all audio gear, you get what you pay for, and the law of diminishing returns applies. If all you want is a circuit that can tell you that an ordinary consumer grade stereo amplifier is working properly, then performance isn't that critical and you can throw together whatever combination of parts you like - but if you want to tell the difference between a $1000 amp and a $10000 amp, a piece of test equipment priced at the upper end of that range wouldn't seem unreasonable.

[Lightages]

To what level of accuracy/noise/distortion do you want to measure? What bandwidth?

You need to answer these questions first before you decide on the equipment. Depending on your answer you might be happy with a a good sound card and Visual Analyzer freeware.
http://www.sillanumsoft.org/

[olsenn]

Look at NwAvGuy's blog: http://nwavguy.blogspot.ca/