Advice Needed for Audio Amplifier Measurement

DonCameron · Post by **DonCameron** » Sun Nov 05, 2006 4:23 pm

We build musical instrument amplifiers. We would like to perform spectral analysis on the signal as it progresses through the amplifier to see where harmonics are injected, etc. Here is roughly the process:

1. Sample instrument signals are fed into the amplifier
2. Signals are recorded in approx 4 places through the amp. Signal levels vary from 100mV to 300V
3. Signals are saved and converted to WAV file format
4. Signals are then post processed using audio spectral analysis software.

And some constraints:
- Signals need to have high sample size to ensure fidelity with analysis software (16bit OK, 24 bit is best)
- Signal aquisition needs to be of high impedance so as to not load amp circuit down

We are currently using BitScope, but it does not have high enough sample size to give us the information we want.

We have also looked at using high end audio interfaces, which have high sample size, but unfortuanately are low-Z input and also require pre-amplifiers.

Can you suggest a product of yours that can help?

thanks
Don

DonCameron · Post by **DonCameron** » Sun Nov 05, 2006 4:24 pm

I forgot to point out, these are all one-shot events.

Michael · Post by **Michael** » Mon Nov 06, 2006 9:02 am

Hello,

Thank you for your post.

Our current best instrument for this type of application is the ADC216. THis is a 16bit scope designed with audio frequency analysis in mind.

With an input impedance of 1 MÎ©, this would sit well in your application.

Further information is available from our website: http://www.picotech.com/audio_spectrum_analyzer.html

Best regards,
Michael

Don Cameron · Post by **Don Cameron** » Mon Nov 06, 2006 2:02 pm

A couple of questions about the ADC216

I see the ADC216 is a parallel port device.

(1) Can you suggest a parallel port to USB converter - we use laptops that do not have parallel ports

(2) What I/O speed does this device run at with a USB converter?

(3) Our one shot sample lebgths are 2 seconds. I expect to record with both channels. With the ADC216 max 2 channel sample rate of 166 kSa/sec and a buffer of 32kSa, 2 secs of data would fill the buffer in under 0.2 seconds. The device would have to stream to the PC to capture the 2 seconds of data, the sample rate would have to be degraded or both. Can you please tell me what happens in this situation?

thanks
Don

Michael · Post by **Michael** » Tue Nov 07, 2006 9:04 am

Hello,

Upon your specification, the ADC216 will not meet your requirements.

You are risght about the buffer and record length, this will not give you 2 seconds.

Even with the USB adapter, you will not get the transfer time required for streaming. Unfortunately, the only instruments we have that comes clos to your specifications is a 12bit scope.
http://www.picotech.com/pc-scope.html

Best regards,
Michael