Need Computer Recommendation for QA404

This may sound too basic, but I plan to buy a QA404 when they are available, and I need some guidance on what type of pc to use with it. I am a Mac person, so I don’t have a pc and I am not a computer-type person anyway. Basically, I want to streamline my workbench and not have a pc or laptop taking up space bench space. My thought is to get a mini-pc that can be placed on the side or behind my existing test equipment and connect it to a small monitor placed on top of other test equipment and the QA404. I have a bluetooth keyboard and mouse I can use with it. My question is how powerful of a pc do I need to buy (speed, internal RAM and HD size)? I think I only need a lower end one. However, I would like recommendations/guidance. Thanks.

Have you considered an Intel iMac?

Last summer I saw that MacSales was having an, uhh, Mac sale of factory reconditioned Intel iMacs. The price for a recent 21.5" model fully equipped with an i7 processor, and the amount of memory and SSD I wanted wasn’t a ton more that buying a separate mini-pc and a new monitor. Better warranty, too.

When it arrived, I discovered that this computer was actually new and was left over from when Apple discontinued Intel iMacs. MacSales just added their own memory and installed their own SSDs. (More on that in a bit.) Checking the iMac serial number showed that it was manufactured during the last month of production.

I installed Windows 10 in a Boot Camp partition. It works even better than I had hoped. Now I can use either macOS applications (Ventura) or Windows with a great screen and all that. My QA401 and QA480 run perfectly on it.

This computer also lets me run the desktop applications for my Analog Discovery 2, a tinySA, a NanoVNA, a Peak Atlas curve tracer, and some other audio test gear. Plus some design software. I’ve been surprised just how much I’ve used it.

You can get factory refurbs for very reasonable prices now. Just be sure that you get one with an SSD that’s compatible with Windows. For some reason, not all of them are.

Anyway, this has all worked for me. YMMV and all that.

I recently set up a Mini PC to take place of a standard desktop to run the QA40x software. I’ve noticed that I get significantly more buffer underrun errors with the smaller, slower PC than I did previously. I have to run the sample rate at 96kHz to prevent errors.

Interesting option. I will investigate. Thanks.

That is what I am trying to prevent. Can you recommend the minimum speed of the computer to precent that?

I’ll have to experiment with the two faster computers I have. I’m off to a trade show for the weekend, but I’ll see what I can learn next week.

Its not as simple as a faster computer. The underruns happen because the USB subsystem did not respond fast enough. Everything from other process running to a shared USB can mess with that. Cleaned up you can get fine results with even an old Atom processor. This app can help determine if you will have problems: Resplendence Software - LatencyMon: suitability checker for real-time audio and other tasks

The issue with using the Resplendence Software to determine if a computer is sufficient is that I would need to first buy the computer in order to measure whether it is suitable (chicken/egg dilemma). It would seem that the best course to achieve my goal would be to know the minimum standards I should look for in a computer such as computer speed, USB subsystem, onboard RAM and whatever other factors are important.

I put the mini-computer minimum requirement question to QuantAsylum and they directed me to this article:

It was helpful, but still didn’t give me specific objective specs to use in selecting a mini-computer for good performance with the QA404 (I need specifics because I am not a computer expert).

However, according to the article, it seems that a critical factor is the speed of the FFT of the computer. Unfortunately, specs for computers don’t give the FFT speed. The article seems to indicate that the computer RAM is critical to the speed of the FFT, but that is not clear.

Can someone give me direction on these factors to purchase the correct mini-computer:

  1. How to determine from published specs if a given computer’s FFT speed would be sufficient for a QA404 (I’m looking on Amazon)
  2. Which specific factor(s) such as RAM or computer speed determine a computer’s FFT speed
  3. The minimum specs of those specific factors that will give me sufficient FFT speed


Hi @ScottRichardson .I can’t give you a detailed answer as you are looking for, but maybe my experience can help you. I have tried the system on different computers, even not very high-performing ones (based on Intel I3, Windows10) and inexpensive ones (such as Lenovo laptops), and I have never encountered any problems in any case. The acquisitions always resulted in smooth and perfect performance. I hope this information can be helpful to you.

The article seems to indicate that the computer RAM is critical to the speed of the FFT, but that is not clear.

Hi @ScottRichardson, the FFT is really a small part of the total acquisition cycle. For example, on a 1M FFT at 48Ksps, it takes about 22 seconds (2^20/48ksps = 21.85 seconds) to acquire the signal. That is is physics, and nothing can change that. After the data is pulled in, it takes about 3 seconds to process the FFTs. These are huge FFTs. My guess is a low-cost fanless PC like the article would take 5-10 seconds.

As you drop your FFT size down, everthing gets faster. So, a 32K FFT would take 682 mS to capture and 93mS on my desktop to process, and probably 300-400 mS on a low-cost fanless PC. I just timed my desktop and in 20 seconds it captured 25 waveforms, so 1.25 updates per second.

For memory, the memory consumed by the QA40x app might go up to 400Mbytes or so during the massive FFTs. So, if you are trying to run on a 1G or 2G machine, it might be an issue. But finding an entry level machine with less than 4G anymore is probably pretty difficult.

I can try again on a low-cost test bay computer tomorrow and report back the number of cycles per second for a given FFT size.

In short, I think a modern low-cost fanless PC with 4 GB will run the app well.

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Hi @ScottRichardson, I just checked on test bay 2 and for a 32K fft it gave 23 waveforms in 20 seconds. So, pretty close to a desktop. For a 1M FFT, it took 9 seconds to process in addition to the 22 seconds to acquire. So, about 3X longer for the FFT processing, but overall just 25% longer to capture and show a 1M FFT

Most working FFT sizes will probably be 32K to 64K.

The test bay 2 computer is a fanless Intel Celeron N4000 @ 1.1 GHz with 4GB of RAM. The PC maker says burst up to 2.6 GHz. I’ll assume the 2.6 GHz is marketing fluff. An Intel Celeron N400 @ 1.1 GHz has a cpu passmark of 1400 or so (single thread rating of 1039).

The N4000 computer is 2020 vintage, and not sold anymore. There is a $150 Intel N5095, with 12GB of DDR and Windows 11 for $150 on Amazon. This has a passmark of 4040 (single thread 1515).

So, triple the ram vs test bay 2, 50% more speed. Windows 11. Mounts behind monitor.

Perfect! That is exactly what I needed to know! Thanks so much. I guess the only other question is whether I would need a USB hub (that computer has two USB ports) and if the specs of a USB hub makes a difference in performance. I’d like to use a touch screen monitor and I think they may need to be connected to a USB port. If I need a USB hub, this one on Amazon looks like it would work well because it’s the latest generation and it’s shielded: