Even as an electronics novice, for years I have wished I had an oscilloscope to answer the occasional question about some low power device I own. I think I'm ready to buy one for that purpose, but am also propelled by a more specific need: I would like to be able to analyze analog audio signals (~20 Hz to ~20k Hz). Since this is such a narrow band of EMF I am wondering if I would be happy with something on the cheap end of the price ranges.

I want to visualize voltage curves with triggers and in real-time, but also frequency spectrum curves (performance of a speaker at audible frequencies, for example). I am guessing I will need a signal generator with white noise and frequency sweep functions and either a simple spectrum analyzer or an oscilloscope with a properly-featured FET function. (I don't know what those features might be.) I would also like to avoid spending more than $65 or so on a measurement microphone. (I wonder if I can use one of the aforementioned devices to compensate a speaker output frequency curve with a nominalized microphone signal recorded with a signal generator)?

I'm not at all against buying products like an oscilloscope dongle for a PC, but I am really picky about software quality, and I have no sense of how nice the software for these devices is. I'm also picky about looking only at high resolution displays. A 640 x 480 display would probably accommodate everything I want to do with sufficient precision, but I just don't want to have to look at such a display. It needs to look at least like a 96 dpi (standard PC) display, ideally being a retina display (but I'm not expecting to find that in my price range).

This would all be equipment for me to learn on, so I am unfortunately not sure exactly what I am looking for. I am pretty sure I will not grow into needing advanced features on any of the equipment nor measuring 5GHz Bluetooth signals. I'll be lucky if my brain can handle the complexity of the projects alluded to above. All of the equipment should have well-designed user interfaces.

Does anyone have any advice about what I think I want to do, or equipment recommendations? I'd prefer the total cost for all the equipment to be under $500, but I can go up to about $800 without losing sleep.

 

You want to make Bode plots, so you should look for a scope that can coordinate with an AWG (Arbitrary Waveform Generator) to produce them.

I am very happy with my Siglent SDS1204X-E and the associated AWG.

It is a bit outside your budget, though. You can see it here: https://store.siglentamerica.com/product/sds1204x-e-200-mhz/

It will do just about anything you are likely to need, and it can do the Bode plots (frequency response) that you want.

 

Why not use your computer with a good soundcard and one of the many audio analysis programs available. Many of these programs are free and commercial products are available free on a trial basis or at low cost in their basic, stripped-down iterations.
There are also many software audio signal sources available, often for free, on the net.
The problem with most stand-alone or computer connected scopes is they are limited to 8 bits of resolution. That translates to 0.4% readable distortion, if you are lucky. No good for most audio work.
Cheers, E

 

Start with the freeware Audacity on your PC. If that whets your appetite, then consider buying dedicated hardware or commercial software.

 

Depending on the type of purity you need for audio analysis (noise floor, linearity, distortion), I suspect the resolution of the regular oscilloscopes and their built-in FFT may not be enough, as they are usually 8-bit (there is only one that can reach up to 14-bit, the Owon XDS3064AE but the quality of other products in the past from this company left much to be desired).

In this case, you could use a very high quality soundcard attached to a PC and use an audio analyzer software.
https://www.qsl.net/pa2ohh/12audiosa.htm
https://www.qsl.net/dl4yhf/spectra1.html
https://www.audacityteam.org

For THD measurements, a multimeter like the Keithley 2015 can be an option (if found used, so it can fit your budget), as it is a bench multimeter with a very low distortion sinusoidal generator and a THD measurement feature. Other suggestions can be found at:
https://www.eevblog.com/forum/testgear/measuring-thd-on-audio-circuits/

 

@Yaakov, thanks for the recommendation. It isn't too outside my budget if instead of getting the built-in AWG ($268), I got a cheap one ($70)—although I'd have to find out what the SDS1204X-E is doing with the AWG (its connectivity) to know if an off brand one would work. Their cheapest standalone AWG is $248. Since I do not lack space, it seems like that would be a better investment.

@Nykolas, thanks for the wise perspective. I will do this before spending money. I looked into it a while back, but because of your prompt I will look again. Last time I couldn't find any decent software (although @rsjsouza may have just solved that problem for me!). My sound card is already a decent consumer-grade one (Audigy 5/Rx). I even have a $80 computer oscilloscope kit that I assembled. It was underwhelming and I haven't used it in years, but I should dust it off to see if it can do anything for this project. I would learn more details of the components and testing process, if nothing else.

@Alec_t, thanks for the idea. Fortunately, I have no shortage of sound file editors, although I'm sure I would have to learn something new about one if it involved more than opening a recorded sound file. My overall problem with this approach is that I do not trust the quality of any of the components in the testing chain, including my ability to install and configure each correctly. Just because I see something like what I expect to see wouldn't mean it is right.

@rsjsouza, I don't know what resolution I need, but for what I'm doing, precision and accuracy can be fairly crude. It is good info, though, to know that oscilloscopes' FET functions are limited that way.

Thanks all!

 

Try the free Visual Analyser from www.sillanumsoft.org. It is a great package with many options and measurement capabilities. Unfortunately it has some minor bugs and has not been updated since 2014. It helps if you can read Italian! E

 

a properly-featured FET function

FET = Field Effect Transistor

FFT = Fast Fourier Transform.

A low-noise AWG for distortion measurements might be very hard to find.

 

Ha, I have spent a lot more hours thinking about FETs than FFTs. I've never worked with FFTs at all, actually, other than looking at finished graphs.