Is a spectrum analyzer the same as a distortion analyzer?

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No. Do you understand a graphic EQ? Think of a spectrum analyzer as a visual VU meter for each band of your EQ... more or less. It shows you what signal levels exist along the audio bandwidth. It says nothing of how clean the signal is.


A distortion analyzer compares the input signal to an amp with the signal coming out of the amp. It then measures the difference, which is done as a percentage.
 
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Is a spectrum analyzer the same as a distortion analyzer ? I see spectrum analyzers locally but not distortion analyzer.

They're not the same but you could use a spectrum analyzer to measure distortion whereas you can't measure a spectrum with a distortion analyzer. Used, relatively cheap "previous century" spectrum analyzers rarely provide more than 100 dB dynamic range so with such an instrument distortion becomes visible above 10 ppm. But with the help of a notch filter the fundamental could be suppressed 80 dB or more and in that case the spectrum analyzer will be a very useful tool.
 
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Is a spectrum analyzer the same as a distortion analyzer ? I see spectrum analyzers locally but not distortion analyzer.

A spectrum analyzer will give you the spectral content of a signal. You can use this to measure the amplitude of a fundamental frequency and its harmonics. That will allow you to calculate the distortion. Some spectrum analyzers (HP3561, for example) will calculate the THD for you.

They're not the same but you could use a spectrum analyzer to measure distortion whereas you can't measure a spectrum with a distortion analyzer.

Exactly. A distortion analyzer (HP8903 for example) will only give you a THD+N number. It doesn't tell you what the spectrum looks like.

Used, relatively cheap "previous century" spectrum analyzers rarely provide more than 100 dB dynamic range

Often only 80 dB dynamic range.

But with the help of a notch filter the fundamental could be suppressed 80 dB or more and in that case the spectrum analyzer will be a very useful tool.

Or see Bob Cordell's Distortion Magnifier in Linear Audio Vol. 0.

If you want to measure distortion, I suggest getting yourself a good external sound card and possibly an interface for it, such as Pete Millett's Sound Card Interface. Use some software, such as ARTA or REW to measure the signal you're interested in and perform an FFT (Fast Fourier Transform - calculates the frequency spectrum of a signal) to determine the spectrum and the distortion. That'll get you to 100-110 dB dynamic range on a good day.

Tom
 
Hello,
There has been a paper in AudioXpress from june to november 2015, on
how to use sound cards to make audio measurements.
 

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whereas you can't measure a spectrum with a distortion analyzer.

I think this is incorrect. All distortion analyzers I have used can also do spectrum analysis. The sound-card+free software options mentioned above all do spectrum analysis as well.

It's all software anyway; once you have the time domain distortion waveform, easy to change to frequency domain (spectrum) and back; they are two sides of the same coin.

Jan
 
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I think this is incorrect. All distortion analyzers I have used can also do spectrum analysis. The sound-card+free software options mentioned above all do spectrum analysis as well.

It's all software anyway; once you have the time domain distortion waveform, easy to change to frequency domain (spectrum) and back; they are two sides of the same coin.

Jan

In the early 1970s, working at Elektuur, I designed a "real" distortion analyzer. It was on the principle of resizing an amplifier's output in magnitude and phase so that it would cancel the (buffered) amp's input signal. Thus, the residue was the distortion which could be seen on an oscilloscope. The significance of that (easy & cheap) method is that there's no need for a low distortion sine generator! :D
What's even better, you get an impression how the distortion will sound...
A modern system with sound card OTOH is a software version of a spectrum analyzer, no matter the label attached.
 
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In the early 1970s, working at Elektuur, I designed a "real" distortion analyzer. It was on the principle of resizing an amplifier's output in magnitude and phase so that it would cancel the (buffered) amp's input signal. Thus, the residue was the distortion which could be seen on an oscilloscope. The significance of that (easy & cheap) method is that there's no need for a low distortion sine generator! :D

Yes, several people did it that way before we learned how to do it fast, accurate and repeatable in software and it got cheap enough for diy ;-)

Hang a headphone on a soundcard and you can listen to the distortion residual all you like.

Jan
 

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Yes, several people did it that way before we learned how to do it fast, accurate and repeatable in software and it got cheap enough for diy ;-)

Hang a headphone on a soundcard and you can listen to the distortion residual all you like.

Jan

The only disadvantage of the method was that while adjusting the pots, you should hold the breath, not cough, eventually have the windows closed, and have a photographer ready to take a shot at the right moment. But that was before 10 (and more) turn pots became cheap ;-) Using the scope in x-y fashion (THD vertical, input horizontal) was quite instructive.
 
I think this is incorrect. All distortion analyzers I have used can also do spectrum analysis. The sound-card+free software options mentioned above all do spectrum analysis as well.

It's all software anyway; once you have the time domain distortion waveform, easy to change to frequency domain (spectrum) and back; they are two sides of the same coin.

Jan

Modern distortion analyzers can do spectrum analysis, but my old Radiometer BKF6d distortion analyzer can't. It is essentially a true-RMS tube voltmeter with a notch filter (and some additional filters for hum and noise).
 
HP3561, 3562, and 3563 would be the audio frequency analyzers. There may be more. The 3561 is analyzer-only. The 3562 and 3563 have a signal source built in.

The HP8903 would also be very suited to measure the distortion of a tube amp.

The HP3581 can be used for measuring distortion as well, although it's a bit more laborious than just pushing the DISTN button on the 8903.

I have owned or used all the instruments mentioned above. Honestly, I'd look into the Pete Millett sound card interface and use an external sound card. If you really want a stand-alone instrument, I'd get an HP8903 for distortion measurements.

Tom
 
One big problem with early HP analysers (I have a 3560A) is that acquired data or screen plots can't be practically transferred to a modern PC - with a photo of the screen being the most practical outcome.

PS. If anyone has got software to download via RS232 and transfer to SDF and then to any modern display format then that would be great to know about!
 
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