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    the safety precautions around high voltages.

lower cost options for spectrum analyser/ function generator?

Rod Coleman

Member
Paid Member
2004-07-25 6:55 pm
UK
Save your cash!

For audio work a PC is all you need, and some freeware.

I like e-Cat's function generator:

http://e-cat.nm.ru/sinegen/

use the "white noise" function to test frequency response, or individual tones for specific testing

feed the output (line level) into your sound card & see the spectrum with this FFT analyser from Japan:

http://www.ne.jp/asahi/fa/efu/soft/ws/ws.html

A sound card that can sample 96Ks/s at 24bit is good enough for much work, 192/24 is riding first class!

All these survived an Ad-Aware check after loading!
 

kevinkr

Administrator
Paid Member
I use audiotester from www.audiotester.de Quite popular around here and the latest version is really good.

The results will only be as good as your sound card, and it really helps to use something that runs the Via Envy 24 chipset or similar so that you are not limited to 48kHz sample rates. I use M-Audio Transit with my laptop which is limited to 24 bit/48kHz in duplex mode on USB, (USB limitation I believe) and an M-Audio 2496 in the media server which can run at 96K.

I designed and built an interface some years ago to protect the snd card inputs, provide additional attenuation for higher voltage measurements like power amplifiers (0dB, -20dB, -40dB, -60dB), input impedance is 100K, and I have also provided gain on the generator outputs (0dB, +6dB, +12dB) The inputs to the sound card have active clamps that also light overload leds for visual indication that the signal levels are too high - on FFTs this is quite visible anyway, but it is useful to know what is getting overloaded. Operation is via a pair of 9V batteries for low noise with simplicity. The SFDR of this setup with the transit is better than 90dB and the noise floor is somewhat below -100dBv, so it's quite useful in fact. (Not close to the theoretical limits for 24 bits though.) My last hardware based analyzer (a Singer) was hard pressed to produce a SFDR of 60dB.
 

kevinkr

Administrator
Paid Member
Gordy said:
ARTA looks promising:
http://www.fesb.hr/~mateljan/arta/index.htm
...and not so expensive.


Not sure what your definition of "not so expensive" actually means, but at $255 (USD) to unlock and license Arta software, versus about $55 (USD) for audiotester it's no bargain. I can think of a whole lot of other things I would rather do with that kind of money.. :D

Arta will not allow you to save files, set ups or anything else in demo mode. It is seriously good measurement software for room measurements and speaker design. For testing electronics it is total overkill.

Unless you need the additional sophistication of Arta (which I have tried and like) Audiotester will get the job done well and is much less expensive. The latest version is very good, easy to use, and set up.
 
kevinkr said:

I designed and built an interface some years ago to protect the snd card inputs, provide additional attenuation for higher voltage measurements like power amplifiers (0dB, -20dB, -40dB, -60dB), input impedance is 100K, and I have also provided gain on the generator outputs (0dB, +6dB, +12dB) The inputs to the sound card have active clamps that also light overload leds for visual indication that the signal levels are too high - on FFTs this is quite visible anyway, but it is useful to know what is getting overloaded. Operation is via a pair of 9V batteries for low noise with simplicity. The SFDR of this setup with the transit is better than 90dB and the noise floor is somewhat below -100dBv, so it's quite useful in fact. (Not close to the theoretical limits for 24 bits though.) My last hardware based analyzer (a Singer) was hard pressed to produce a SFDR of 60dB.

Kevin,

Do you mind sharing the schematic for this interface?

TIA,

-- josé k.
 

KSTR

Member
Paid Member
2007-07-17 2:35 am
Central Berlin, Germany
Kevin, no need to buy ARTA. Website reads The demo mode of programs is fully functional except loading and saving of files. To "save" a measurement you still can use a plain screen hardcopy. Older versions exist that aren't protected and are fully functional.

LTSpice (a *free* circuit simulation software) also has FFT capapilities, plus a .WAV interface (read and write). It can be used to create and analyse test signals, which may be not as convenient (not real time mode, etc, and you need to put some time and effort into it) as a true generator/analyser, but it's possibilities are not limited in any way -- and it's free.

- Klaus
 
KSTR said:
Kevin, no need to buy ARTA. Website reads The demo mode of programs is fully functional except loading and saving of files. To "save" a measurement you still can use a plain screen hardcopy. Older versions exist that aren't protected and are fully functional.

LTSpice (a *free* circuit simulation software) also has FFT capapilities, plus a .WAV interface (read and write). It can be used to create and analyse test signals, which may be not as convenient (not real time mode, etc, and you need to put some time and effort into it) as a true generator/analyser, but it's possibilities are not limited in any way -- and it's free.

- Klaus

I hear you, but not being able to save files in the program means that you cannot directly compare or take difference curves of sets of measurements done over some period of time. Also I think doing what you suggest (and I've thought of it) to some degree unfairly circumvents the author's right to be paid a fair wage for the use of his work. Since I like to get paid for the work I do I evaluated the software, concluded that it was not immediately needed and am not using it at this point. When I need it I will most definitely pay for it.

Audiotester provides a lot of the capability for a very small fraction of the price and I use my licensed copy regularly.

Very familiar with LTSpice, and use it extensively, I think using it to generate wave files for testing purposes is not that user friendly.. Great otherwise though...


;)
 
I have a full-featured linux spectrum analyzer, free and fully open, that works more in the style of a traditional bench tool than baudline (which is still a great program, and I use it regularly myself for music).

Source is at http://svn.xiph.org/trunk/spectrum

I'm in the middle of updating it (it's actually quite an old program I never finished at the time) to work niggles out of the automated testing modes. It also needs a nice detailed webpage to explain how you'd use it to the average newbie getting started. It works fine now if you want to go get it, it just needs more polish to be a real tool you can use with no real handholding. I've been polishing it up for about a week now.

It'll be getting its own thread as soon as I'm a little happier with the noise suppression in the automated testing modes and reenable the automated THD testing. If you're using a consumer sound card to drive/sample for it, I recommend a high-impedence opamp voltage follower to buffer the inputs.

Oh, and if you want a trustworthy program to do the sampling (that is guaranteed not to skip), http://svn.xiph.org/trunk/rtrecord will give you what you want. It will happily talk to the analyzer over a pipe, and also gives you a nice standalone app for those times when you want to use the computer as a bulletproof standalone sampler/hard disk recorder.

(attached a better screenshot of the analyzer doing something useful: A response/phase plot of a Cinemag CMLI-15/15B with a line impedence of 50 ohms, an output load impedence of 15kOhms, collected realtime using a pink noise sample, played and sampled using an emi2|6 with inputs buffered by a TL3474 opamp voltage follower. In short-- good results for equipment only a notch above 'BestBuy' and not even as good as you'll get from the Apple Store.)
 

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kevinkr said:
I use M-Audio Transit with my laptop which is limited to 24 bit/48kHz in duplex mode on USB, (USB limitation I believe)

My eMagic boxes are USB and I run them at 24/96 full duplex.

Oh, related question-- Anyone got a better opamp for the input buffering than the Linear LT1115? It appears to be the nearest thing us mortals can hope to an ideal audio opamp for $5. High slew, low distortion, low noise, super low bias current.
 

Gordy

Disabled Account
2006-11-02 6:15 pm
xiphmont said:
I have a full-featured linux spectrum analyzer, free and fully open, that works more in the style of a traditional bench tool than baudline (which is still a great program, and I use it regularly myself for music).

Source is at http://svn.xiph.org/trunk/spectrum

I'm in the middle of updating it (it's actually quite an old program I never finished at the time) to work niggles out of the automated testing modes. It also needs a nice detailed webpage to explain how you'd use it to the average newbie getting started. It works fine now if you want to go get it, it just needs more polish to be a real tool you can use with no real handholding. I've been polishing it up for about a week now.


Keep up the good work.
 
Re: What soundcard?

duderduderini said:
My pc has a rudimentary on board sound card to be polite.
What soundcards do some of you use?
The laptop i have has a firewire port but only usb 1.1 or i have a desktop with pci
Thanks

Most USB sound cards are still usb 1.1 because the USB2.0 audio profile has not yet been standardized. Anything claiming to be a USB2.0 compliant sound card isn't really-- it's using USB 2 and its own proprietary drivers that may or may not work the way you expect.... (to be fair, the spec is taking a long time and a few are using draft versions of the spec)

I use the eMagic USB cards as cost effective and well behaved. There's nothing that special about them except they can be clock-locked together. And since Apple bought the company that makes them and then discontinued all their products except Logic, you can find them used/NOS very cheap. They were $300 new, I bought my last two for $35 each.