Spectrum analyzer vs. FFT capability

[SoaDMTGguy]

Simple and not too much money, and provides enough distortion information for most hobbyists:

Howto - Distortion Measurements with REW

Thank you! This was exactly what I needed.

 

[nigelwright7557]

If I want to see the waveform of my fundamental frequency and the distortion, do I need a spectrum analyzer? Getting an oscilloscope that can do FFTs will show me the magnitude and harmonic characteristics of distortion, but I assume it can't show me the waveform like above?

You can get scopes with FFT display too.
I designed my own scope + spectrum analyser for audio.
It works via USB to pc display.

 

[SoaDMTGguy]

You can get scopes with FFT display too.

This was my thought, but others have said the resolution wouldn’t be sufficient. I’d prefer to have a dedicated piece of hardware for doing measurements.

 

[jan.didden]

There ARE scopes with enough resolution for useful audio FFT. I think they start at about $ 12k 😎

Jan

 

[nigelwright7557]

Here is a shot from my scope/spectrum analyser.

 

[1audio]

I have not had really good value from the Siglent FFT. It works and you can get a rough idea of the spectrum but nowhere near as useful as a PC soundcard. The Picoscope FFT is much more useful. Still the PC soundcard has worked better. You have numerous choices for software with a PC.

 

[SoaDMTGguy]

What interface do you use for your PC? I was looking at the Scarlet.

 

[1audio]

The Scarlet is a fine choice. I have a collection;
EMU 0404USB
Emu Tracker Pre
Emu 1616M
ESI Juli@
RME PCI Hammerfall
Lynx L22
RTX
Each has specific benefits but they are all useful.

 

[trobbins]

Nigelwright7557, perhaps better to change the scope plot y axis to dB (rather than V) and the x axis to decade to present a reasonable comparison.

 

[Steve3J]

If I want to see the waveform of my fundamental frequency and the distortion, do I need a spectrum analyzer? Getting an oscilloscope that can do FFTs will show me the magnitude and harmonic characteristics of distortion, but I assume it can't show me the waveform like above?

I have a piece of test equipment that has Spectrum Analyzer, Receiver and FFT capability in one unit on my day job. This is in the 10 kHz to 18 GHz range but the principle is the same.

Each has is optimum application.

The FFT is very fast. It can capture and process the information in seconds.

The tuner is second but it does not capture all of the information in the complete range selected. It looks only at discrete frequencies.

The Spectrum Analyzer is typically the slowest but affords maximum information, sidebands, spurs, harmonics etc.

A scope with FFT function should be more than adequate for your analysis.

 

[Mark Tillotson]

Scopes are often simple 8 bit flash-ADCs, that's very limiting for audio distortion measurement.
Soundscards usually have 24bit sigma-delta ADCs with noise-shaping.

 

[SoaDMTGguy]

What is “noise shaping”? Does it give the noise a bigger bust and slimmer waistline? 😛

 

[Mark Tillotson]

This might help. Its pretty technical. The quantization noise is magicked into the ultrasonic part of the spectrum.

Attention Required! | Cloudflare

 

[nigelwright7557]

Scopes are often simple 8 bit flash-ADCs, that's very limiting for audio distortion measurement.
Soundscards usually have 24bit sigma-delta ADCs with noise-shaping.

I use 10 bit a2d in my usb scopes.
The noise on the screen is then a lot better than 8 bit scopes.