Comparing PC FFT Program ARTA Software to HP 3580A & iPhone FFT Program

It certainly seems the FFTanalyzer is the way to go to get frequency domain information of audio frequencies. Low frequencies, i.e. 20 Hz and even lower are displayed on the FFT analyzer much quicker than the traditional audio frequency spectrum analyzer. Above about 5 KHz I do experience the FFT analyzer disagreeing more and more as the frequency rises with the THD display of the Tektronix AA501 and the HP 8903. 50% disagreement occurs with a fundamental frequency of about 16 KHz.

[@marckeisler4878]

Raymond, I want you to know how much I really appreciate the content of your videos like this. You've answered a question I've wondered for quite some time. It was so nice to see this demonstration.

[@Pentode3000]

ARTA is awesome. I mainly use it to measure Loudspeaker frequency response and it can do so much more. If you put a loop on the sound card you can measure the frequency response of the soundcard and also use it as a correction file if there are some deviations from a linear response. Usually this is the case with onboard soundcards. Of course this is just a worst case method as you should use good equipment in the first place. The external or good internal devices are very linear these days at least in the audio range. And of course you can measure any amps frequency response. Not an easy program at first but worth every cent and there is a ton of information about it in the web so it is really rewarding getting into it. Great video again!

[@stoneeh]

Good stuff. Linear averaging gets the noisefloor smoothed out even further; it stops the measurement after a certain max number of averages, but you can set that to up to 100000, so no worries there :) I currently use ARTA's SPA mode for example for multitone distortion measurements of loudspeakers, with an output filter representing the spectrum of music (EIA-426B). Lots of good work put in by Mr. Mateljan. And there's also a extensive documentation available, by Dr. Heinrich Weber, called the ARTA Handbook.

[@ElPasoTubeAmps]

Thanks - I looked up ARTA User Manual and this is what I found - very nice. artalabs.hr/download/ARTA-user-manual.pdf

[@micomrkaic]

Another superb video. Many thanks.

[@59seank]

Pretty amazing. I never thought an iPhone was that capable.

[@djfrank59]

Hi David! This was an interesting video. I actually downloaded the Arta software (free version) to play with it a little. I think for me, this is great for out in the field. a lot easier than lugging a CRT spec analyzer :). Carrying that stuff around using public transportation can be an adventure...especially if I have to lug it up 3 flights of stairs doing a service call at a recording studio. For the shop, I'll stick with my good 'ol analog/CRT gear :) But it is pretty amazing. Keep 'em coming. :)

[@ElPasoTubeAmps]

I agree, Frank. I have had to carry an oscilloscope, network analysis tools and calibration stuff around on a plane before (long before 911...) but I was so much younger and seemed to never get tired. I loved doing it so much. I sure wouldn't want to do it now. I think the only extra device you need besides your PC, assuming you have a sound card that you are happy with already in it, is an attenuator. From my little experience with it about -30 dBm is what most sound cards seem to like. I don't really know what I got by buying a license. As far as I know everything works the same. There is another product out there called SpectraLab that is pretty expensive and only a 30 day trial. I used SpectraLab many years ago on a Win 98SE computer. I made a CD of the program just after installing everything, including SpectraLab and every 30 days would have to disk-wipe the HD and then "ghost" a copy back on. The DoD disk wipe was necessary as a disk format would not wipe out something that the program must have written in the master bit table or somewhere that a format would not wipe out. That was my first audio spectrum analyzer. I believe it ran on a 80286 processor. Remember that long ago? :-)

[@djfrank59]

Wow! 286 brings back memories! I had one back in the day. Believe it or not, I use a few audio editing programs made by NCH software that I have to re-install every 14 days, but I don't have to wipe out the HD...I simply go into the windows registry and delete any keys that point to the program and I'm able to do a fresh install. Yea, at my age, i don't want to lug heavy gear around...it seems like yesterday I could carry a house...not anymore. :)

[@jwrtiger]

Hi, I checked the Arta website and it looks like if you do not pay for the license you can not save or load files. Here is the exact wording from their site: "If you have no license key, you can freely use this software only in a demo mode. The demo mode of programs is fully functional except loading and saving of files." On another note I think you have the Behringer UMC404HD (four channel). I noted in their spec sheet that the UMC204HD (two channel) has better dynamic range and is a little cheaper. If you don't need the 4-channels and can get by with 2-channels the 204HD might be a better purchase for the Arta software. I order the 204HD so we shall see... Again thanks for the videos on this topic, you do a great job.

[@ElPasoTubeAmps]

I really appreciate you telling me this. I have looked at the two channel Behdringer and see it is only about $59. I would have bought it or even a one channel if it had been available. Please do let everyone know how your two channel device turns out. One thing I see over and over with this program and the devices that I have is that the higher order harmonics are less and less accurate in their amplitude as we go up in frequency. The second and third harmonics are about two and four dB different from the HP 3580A which I am pretty sure explains why THD readout is significantly incorrect at 10 KHz and above. The harmonic amplitude gets more and more in error as the frequency increases. When both my Tek AA501 and HP 8903 agree I can't ignore them and the ARTA software and hardware that I use for the FFT device does not agree. I am disappointed in that and I want something better. I think the problem is in the hardware and not the ARTA program.

[@EJP286CRSKW]

+ElPaso TubeAmps You're getting closer and closer to the bandwidth limit of the hardware, so it attenuates higher harmonics accordingly. 192kHz sampling only gives you 96kHz bandwidth, which is really not enough for audio SA unless you confine yourself to lower frequencies. It only gives you four harmonics of 20kHz for example.

[@edvaioli7340]

Hi El Paso. I'm curious about the physical connection to the soundcard since I didn't see any BNC connectors. This seems to be a very nice, relatively low cost solution for someone like me who is just a hobbyist. Thanks for taking the time to share your experiences. And what is the model of the Behringer you are using?

[@baghdadiabdellatif1581]

Great work 👏 Name of i phone application plz

[@wmk0100]

Good video, what did you use to isolate or attenuate the signal going to your computer?

[@ElPasoTubeAmps]

I honestly don't remember as it was six years ago but I probably put it on the output of a 10K attenuator pot I have hanging off my "break out" BNC box. Not sure if you can see it in this video but it is where I bring all instruments together so I can measure everything at once. Practically anyway to attenuate the signal down to a few mV should work using a pot.

[@wmk0100]

@@ElPasoTubeAmps thanks

[@DAVIDGREGORYKERR]

the new sounds cards should be able to get 38400khz, if you have an AMD PHENOM II X6 you might be able to use the 32768 point FFT.

[@ElPasoTubeAmps]

This one will go to a sampling rate of 19.2K and an FFT of 131072. It goes to 100 KHz but has a rise in the apparent noise floor because of the DAC, as it has been explained to me. I have found that for looking at 5 Hz it is much better to use a sampling rate less like 44100 (that is as low as this sound card will go) and highest FFT. The pulse width is then from 4.4 Hz to 7.4 Hz wide (4 Hz) and looks like something that could be used. The higher FFT rate seems more important on the lower frequencies - to give a low RBW. On the other hand, who really needs a RBW of 1 Hz for a 10 KHz signal?

[@nathanhaltman7235]

+ElPaso TubeAmps Have you ever considered the HP 3585? 20 HZ to 40 MHz. 3Hz RBW. Tracking generator. 50/75/1M ohm inputs?

[@ElPasoTubeAmps]

I have considered that HP model and also the ones that go down into the milli-hertz region. One thing that I have found out about SA's is that the very lowest end of the specs is often times hard to attain and this SA goes up to 40 MHz - it's really not an audio frequency SA. 20 Hz is actually not low enough for audio, in my opinion. The 3580A goes to 5 Hz and will take eight (8) minutes to make one sweep. With these FFT analyzers, it is easy to do 5 Hz (with RBW in fractions of a Hz) and is so much faster than a swept-tuned analog SA. I think the FFT analyzer is the way to go in audio not that I don't love the magnificent HP equipment of yesteryear but all that equipment is approaching 40 years old and some day it is going to quit and may not be repairable. The new FFT equipment can be had for less than $250 (maybe even free) and it has a much lower noise floor so you can easily see signals well below -85 dBm that is the limit of the 3580A.

[@nathanhaltman7235]

+ElPaso TubeAmps With every thing going USB, I may have to buy a computer for the bench some day. For some reason I prefer the look, and feel of dedicated test gear. It is nice to have buttons and knobs in the physical world.

[@ElPasoTubeAmps]

I prefer dedicated equipment also but things are changing at an accelerating pace. Luckily, much of this stuff is made in China for pennies of what it cost many years ago and it actually gives us good answers. It reminds me of a cartoon I have seen just a few times. An old lumber jack with an ax and a pencil-pusher geek with a chain saw get into a contest of chopping and cutting wood. In the spirit of cartoons they start chopping and cutting and the pile of wood quickly goes miles high into the stratosphere for both of them - Then another little fellow comes out with a ruler and measures both piles and the pencil-pusher geek has a pile 1/4 inch higher than the lumber jack. That is the advancement of technology.

[@stefanvaneylen9488]

Hi! i am interested in buying FFT spectrum analyser software to run on my macbook. i work on mostley tube-amps and want to look at the audio spectrums. my question: how do you connect the software running on the laptop to a tube-amp for example a fender deluxe reverb? what extra interface devices and probes do i need? thnx! Stefan from Belgium.

[@ElPasoTubeAmps]

Hi Stefan, I connect some form of attenuator across the dummy load and attenuate it down to a level that doesn't overload the front end of the USB sound card. There is no special probe needed. If you are running low power you can use a 600 ohm variable pad or one calibrated in dB attenuation but if you get up around 100 watts you will dissipating over one watt in your attenuator so you have to be careful at high power not to damage your attenuator as most of them are rated at one watt. What works well for me is simply a 10K pot across the 4, 8, or 16 ohm dummy load that the amplifier is running into and just pick off a very small portion to put directly into your USB sound card. That is the simplest way if you do not require to know an exact calibrated amount of attenuation. I hope this helps.

[@stefanvaneylen9488]

hey! thnx a lot for clear explanation. i really appreciate this. i go now first order a usb soundcard and download the limited fft free software and use some kind of attenuater and see how far i succeed. i get lots of Marshall 100w amps on my bench so i need to be carefull not to burn up my soundcard :-)...thnx man!!

[@dennisqwertyuiop]

did not catch the usb sound card ? name

[@ElPasoTubeAmps]

I have used two USB sound cards. One was Focusrite 2i2 and the other a Behringer.

[@jpdesroc]

What version of ARTA do you have ? I was about to buy a HP 3580A but ...

[@ElPasoTubeAmps]

I don't know the version I have but you will just download the latest version off the web. I suggest you take a look at the SpectraPlus and you can make some decisions from what you find on the web. As for the HP 3580A, it was the cat's-meow in its era but at -80 dBm that is the tiniest blip on the screen and to display 10 Hz you have to let it scan as low as 200 seconds per division (2000 seconds per sweep). On the other hand, it is a lab quality instrument and if want to look at frequencies in the KHz range up to 50 KHz its sweep time is acceptable. Hope this helps.

[@ElPasoTubeAmps]

Version 1.8.5 is the version I have.

[@jpdesroc]

Thanks !

[@endremurti]

hy , what hardware do you use for probing?

[@ElPasoTubeAmps]

I use an external USB sound card like, in this case the Behringer or maybe a Focusrite or whatever you might have that the ARTA software can connect to thru the USB port. I am confident it can find any USB unit. If the external sound unit has mic input you can use that for high gain, if you need it, or use the line level mode for higher voltage levels from the device you are measuring plus some attenuation network, etc. to get the input signal to a level the sound unit can handle.

[@endremurti]

@@ElPasoTubeAmps ok, can i use such thing for measure the gain of smps ? I develop resonant converter whixh need to explore the mag gain

[@ElPasoTubeAmps]

@@endremurti Sure, if you can measure the input accurately and then the same for the output or you can do 10*log of the power ratios with a volt meter. I am not sure the dynamic range of this FFT device is adequate to measure input accurately but I may be wrong. You will just have to try. I can give you an example. Suppose your driving voltage is 1.5 volts across an input load of 500K (you convert this to input power and get 4.5 microwatts) and your power output is 50 watts, the gain would be 10*log (50/4.5E-6) = 70.46 dB. Hope this helps.

[@micomrkaic]

What is the iPhone program you use?

[@ElPasoTubeAmps]

It is an app called, "Audio Spectrum Analyzer" I might also add that you need a 4 contact type male connector to use with the iPhone and not the standard 3 connection stereo type used in a stereo headset with a microphone.

[@micomrkaic]

Many thanks. Your videos are great. I learn so much from them.