Products > Test Equipment

Audio Analyzers (but not a toy)

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jasonRF:

--- Quote from: KungFuJosh on June 28, 2023, 04:57:28 pm ---
--- Quote from: danils on June 28, 2023, 04:13:53 pm ---In my view it's unclear if the OP is looking for a spectrum analyser working in the audio band or a so called "audio analyser" with all the audio related measurement function.

--- End quote ---

What I really wanted was instant gratification bode plots (for things like guitar pickups, and speakers), but I'll stick with my scope for now, and eventually try out the software based stuff.

--- End quote ---
If/when you decide to try out the software-based stuff, in addition to REW you might want to look at a software package called ARTA as well.  It has a number of different bode plot options to choose from, including ones that are essentially real-time using swept-sine or noise waveforms.  I haven't used it, but from the documentation it is written by someone who understands signals and systems pretty well. 

jason

Smoky:
I'm getting the hang of using the 35660A, 35665A, and the 3588A when fixing stereo and radio projects.

Crossovers and filters can be checked to see if channels match by using the built-in source or your frequency generator.

Set the span and the marker's location and your off and running.

The analyzers are self-calibrating and easy to use but I'd recommend that the analyzer's power supplies be rebuilt.





KungFuJosh:

--- Quote from: trobbins on June 29, 2023, 04:01:55 am ---Soundcard and REW provides frequency response of amplitude and phase, from 2Hz to 96kHz. 

--- End quote ---

I assume you're referring to hardware limitations depending on the sound card in use? Or does REW have frequency range limits?

trobbins:
REW has a nominal sine signal generator range from 1Hz to half the sampling rate of the soundcard used (so for nearly all soundcards that means 96kHz upper limit).  The impedance measurement also uses a sinewave frequency sweep, which is from half the lower setting frequency, which afaik is 0.1Hz (I beta tested this a few years ago when I asked about lowering the low frequency limit to get a better understanding of choke impedance below the previous limit of 2Hz).

Hardware limitations mean that the soundcard and probes will likely have increasing roll-off below about 10-20Hz, and above about 40-50kHz, which is compensated for by using a calibration curve to get a net flat response for loopback, although the DUT doesn't experience a flat response signal and the compensation starts to introduce noise/artifacts depending on the level of roll-off being compensated.  The low frequency response of a soundcard may be able to be modified (eg. by increasing value of any coupling caps, or removing the coupling caps and managing for a dc input).  The high frequency response may be modified by adjustment of probe compensation or tweaking the compensation circuit in the probe.

nenea dani:

--- Quote from: trobbins on June 29, 2023, 04:01:55 am ---
--- Quote from: KungFuJosh on June 28, 2023, 04:57:28 pm ---What I really wanted was instant gratification bode plots (for things like guitar pickups, and speakers), but I'll stick with my scope for now, and eventually try out the software based stuff.
--- End quote ---
Soundcard and REW provides frequency response of amplitude and phase, from 2Hz to 96kHz.  Compensation is automated for 2Hz to circa 10-20Hz, and from circa 40k to 96kHz where the soundcard and probes and test rig may have a non-flat response.  That is, as I understand it, your instant 'Bode' plot.  For some esoteric audio applications where feedback related stability is a concern, the 96kHz upper limit can be too low, as measurement of gain and phase margins require a wider bandwidth (and hence a need to go to something like a Picoscope 2206B with FRA software to extend Bode plot bandwidth to 1MHz).


--- Quote from: nenea dani on June 28, 2023, 10:37:33 pm ---  Focusrite 4i4 has only one linear source and about 5 in switching mode, so the sinusoidal signal is not extremely clean in generator mode. I am attaching a photo for compliance, although one of the sources is masked by cables. With REW I noticed that after 25kHz the signal drops and above 30kHz it starts to have phase noise. In loop mode, the oscilloscope seems to provide a synthetic signal because everything seems perfect.
--- End quote ---
I'm unsure what you are describing.  You seem to infer that internal circuitry of the 4i4 is adding spurious signals to a generated sinewave, but only show a photo rather than a loopback response (!?)  Your test setup may need some refinement, although it would be expected that a raw loopback would show the effects of high frequency roll-off from either the DAC side, or the ADC side, or your interconnection, which is why REW allows you to calibrate out such droop.

--- End quote ---

I am attaching a diagram with the output from 4i4 for 20kHz sine somewhere at 1/2 FS with the specification that it is not in the loop. Everything is satisfactory, but higher in frequency we have artifacts. I am attaching two more diagrams, one up to 250kHz and the next up to 2.6MHz. The noise generated by the switching sources can be clearly observed, although it is possible that some artifacts have another origin. The noises in the last diagram do not disappear if the signal is off, but are proportional in any situation to the level of the master potentiometer. These disturbances are best seen with the oscilloscope on a rectangular signal because they have about 12-15% of the useful value. The spectral components used in the composition of the rectangle are stable over time, but the noise of the switching sources wanders continuously. I use an LC filter with fc =136Khz, N=7 at the output of Focusrite to clean all the radio frequency when I need a sine wave 20Hz-100kHz. After all, it's a 200 Euro sound card and for the hobby it's just fine.

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