Products > Test Equipment
Audio Analyzers (but not a toy)
KungFuJosh:
--- Quote from: pdenisowski on July 04, 2023, 11:35:31 am ---Edit: looks like you can still pick up a used one from Ebay for 15-20K USD :)
--- End quote ---
I offered them $200. For some reason they didn't accept. 🤷🤣
nenea dani:
--- Quote from: trobbins on July 04, 2023, 12:05:49 am ---
--- Quote from: nenea dani on July 03, 2023, 07:56:40 pm ---Sorry for rectangular and FS. I had in mind square wave and Full Scale respectively. Now I have calibrated the board, I have disconnected all the unnecessary devices nearby and the LED lights. I use RG316 cables and everything is well shielded. I am attaching two diagrams with a 20kHz signal / around 55mVeff measured with the oscilloscope at the input of the analyzer and then removed. I immediately connect with the generator off and it can be seen that the switching sources are still there or somethings. You are right that devices connected together can influence each other and that radio frequency artifacts do not matter in audio. However, some high-performance amplifiers can exceed 500Khz and I heard that ten times the band limit is needed for tracking tests phase change. In short, to work correctly between 20Hz and 20kHz, it must have minimum attenuation between 2Hz and 200kHz.
--- End quote ---
Was the last plot made with the same test connections as the first two plots, but just with the soundcard not being asked to generate the 20kHz sinewave tone?
Did you do a reference plot with the same equipment and test connections in place, but the soundcard itself unpowered ?
Can you elaborate on what "ten times the band limit is needed for tracking tests phase change.", as I'm not sure what 'tracking tests phase change' means.
Do you make tests that use the 4i4 to generate signals and apply them to equipment, and have the Sigilent scope connected at the same time for measuring performance of the equipment in the frequency range beyond that of the 4i4 test signals, and is that what you are concerned about?
--- End quote ---
In fact, I did the last test with the generator connected as in the first two tests, but switched from on to off. I also did tests with the 4i4 board disconnected from the USB and indeed there are artifacts at about 100Mhz where it probably receives local FM stations and something else around 1.17Mhz but no more. I want to start a real analyzer to properly investigate. As soon as I find out, I'll let you know the result. I understand that this Siglent that I am currently using, is a teaching device and is not 100% reliable. This SA does not behave very well between 9 and 75Khz and therefore in TG mode it has the possibility of normalization for "correction". For now, I have to take out of the warehouse a 25Kg Systron Donner ultra-old mastodon, but rebuilt and tested. I don't want to use the 4i4 board at more than 20Khz because the manufacturer only guarantees up to this point, but I'm intrigued by the noise that appears at the same time as the useful signal and which is dependent on the master level and that's why I think it comes from inside.
I abandoned Focusrite and now I'm testing a white noise generator that seems to be fairly constant between 20Hz and almost 100kHz.
Regarding the 2Hz-200kHz or even 500Khz spectrum, this is the range on which the amplifier must be checked. "Such frequency extension gives the possibility to maintain the phase errors to a very low level". There are many articles on the net and the first one I found quickly is http://www.audioanalogue.com/en/maestro-monoaural/maestro-monoaural-se-power-amplifier
Surely this issue is known to those who build hi-fi, but my expression was not correct because I am just an audio hobbyist.
Doctorandus_P:
My preference would also be to use a (high-end) sound card.
If you want a "stand alone" device, you can also combine it with some tablet PC. There are plenty of second hand of these,
trobbins:
nenea dani, this is all quite interesting, and I commend your efforts.
The various dc/dc on the soundcard I use (EMU 0404 USB) causes a known corruption within the 96kHz bandwidth of its measurement spectrum, and users identified a way to suppress that by re-routing a signal line away from a dc/dc internal to the soundcard. For the audio work I do, which certainly extends to 96kHz, and beyond, I know there can be some spurious signals down in the weeds on one channel of the soundcard - which can either be overlooked, or the other channel used (some users find that noise aesthetically displeasing, even though it typically doesn't detract from the measurements they are making).
When I need to extend measurements beyond 96kHz, which I certainly do for Williamson amps and typically have to go out past 500kHz to assess feedback gain and phase margins, I use a separate signal generator and a scope and some voltmeters that have enhanced bandwidth, and so there is no opportunity for the soundcard to pollute such measurements. So I'm intrigued as to what type of measurement situation could be corrupted by a soundcard emitting noise well outside its nominal measurement bandwidth. Are you envisaging that the soundcard would be in use at the same time as when measurements were being made by other equipment (which could be corrupted)?
Ciao, Tim
nenea dani:
--- Quote from: trobbins on July 05, 2023, 09:38:22 am ---nenea dani, this is all quite interesting, and I commend your efforts.
The various dc/dc on the soundcard I use (EMU 0404 USB) causes a known corruption within the 96kHz bandwidth of its measurement spectrum, and users identified a way to suppress that by re-routing a signal line away from a dc/dc internal to the soundcard. For the audio work I do, which certainly extends to 96kHz, and beyond, I know there can be some spurious signals down in the weeds on one channel of the soundcard - which can either be overlooked, or the other channel used (some users find that noise aesthetically displeasing, even though it typically doesn't detract from the measurements they are making).
When I need to extend measurements beyond 96kHz, which I certainly do for Williamson amps and typically have to go out past 500kHz to assess feedback gain and phase margins, I use a separate signal generator and a scope and some voltmeters that have enhanced bandwidth, and so there is no opportunity for the soundcard to pollute such measurements. So I'm intrigued as to what type of measurement situation could be corrupted by a soundcard emitting noise well outside its nominal measurement bandwidth. Are you envisaging that the soundcard would be in use at the same time as when measurements were being made by other equipment (which could be corrupted)?
Ciao, Tim
--- End quote ---
It seems that we don't have to worry about what happens above 100kHz if we use the Focusrite board only up to a few tens of kHz. Indeed, the sine signal appears polluted and this makes us think, but now I understand that it does not affect the measurements. I'm trying to reach 100kHz in analog mode and that's why I built an up-mixer that moves the whole 20Hz-100kHz spectrum to 1,000,020MHz-1,100.000Mhz and thus there is no longer a problem that SA starts with 9kHz. In this way, I see everything that happens in almost 80dB. I still have to build a pure sine generator at least for 25KHz-100kHz or lower(1kHz-100KHz) and synchronize it with SA. For now I'm struggling with a white noise generator that doesn't allow a precise measurement for fc(-3dB). I still have subtle problems that don't allow me to go below 15-16Hz because I have some phase noise from the local 1MHz oscillator, but I really don't do the performance, just a hobby. I am very careful with the noise and that is why I use multiple decouplings including tantalum and only linear sources. Even if my work is in the area of switching sources here in audio, I don't even want to see it. Sometimes I use an ultra low noise LDO, but here it was not necessary. I cannot connect the SA Siglent input in parallel with the oscilloscope input because the first disturbs the second in the sweep rhythm. However, I think that the Focusrite board is not disturbed by SA Siglent.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version