Crazy results using Cable or Mic attached to sound card

John Mulcahy

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Afraid not. Perhaps best to make sure a basic loopback measurement works normally before trying the impedance rig, if you haven't already checked that.
 

Elmojo

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I thought I had done that multiple times, but perhaps not correctly.
Is there a guide or video for that process somewhere?
 

John Mulcahy

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There isn't a lot to explain, connect output to input and make a measurement. Attach the mdat file for review.
 

Elmojo

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Hence my frustration.
I've found really very little actual explanation of how to do some of these steps.
For example, when connecting output to input, as you say, what cable should be used?
Is this with the regular measurement cable or a special 'calibration' cable that's wired differently?
If it's the regular cable, should the leads be shorted?
Is the sound card calibration necessary? If so, is it done with the same cable as the circuit cal done on the measurement screen?
There are a ton of little details like this that I've never seen demonstrated in a way that I can easily follow.
As much as I hate to admit it, I guess I've become part of the YouTube generation that needs to see things done to fully grasp them.
Also, when I connect to my external USB sound card, the noise floor (sorry, probably wrong term) as shown in the input graph on the measurement screen is at about -32dB. When I connect the same cable to my laptop, it's down around -61dB. Is this significant? I assume so, but can't figure out why or how to correct it.
The levels and results I seem to see on the preferences page don't appear to agree with what gets reported on the measurement page in some cases. For example, I can run through the 'check levels' process on the prefs page, and sometimes get things to look pretty good. However, when I go over to take a measurement and click the [check levels] button there, it tells me the ref in level is very low. Sure enough, if I ignore it and try to take a measurement, I get a similar message, and the graph is pretty much flatlined.
This is all addiing up to me not being able to make this work, and it's baffling me as to why. I really don't feel like it should be this hard, at least the early 'getting started' part.
 

John Mulcahy

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There is nothing special about the cable used for a loopback, it is the same as would be used to connect anything to the interface.
The leads should not be shorted.
Soundcard calibration is not used for impedance measurements, they have their own calibration steps. For SPL measurements it can be used if the input and output are both on the same interface. It uses a loopback connection using a normal cable.

What external USB soundcard are you using?
What kind of connectors does it have?
What kind of connectors does your laptop's built-in card have? Is the input a mic/line or mic only? If mic only it isn't suitable.

Problems tend to be due to fairly mundane things, like using a mono connector in a stereo socket or stereo in mono. I suggest you begin by using only the signal generator (1 kHz tone) and the Levels meter with a loopback cable and make sure:
  • that the levels shown on the inputs are sensible when the generator is not running (should be very low, typically below -80 dBFS)
  • that when the generator is turned on using the left channel as output only the left input channel level increases, ditto when using the right channel
  • that the input level follows the generator level. There will often be an offset, depending on the settings of the input and output level controls, but adding 10 dB to the generator output should add 10 dB to the input level
 

Elmojo

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Thanks John, I appreciate all the info. That would have been super useful a week ago when I started this twisted journey. :)
My wife finally saw my frustration last night and pulled the plug, by which I mean she bought me the Dayton DATS box.
I think there's something wrong in the sound card(s) I'm using, or the way I'm trying to configure them, or both.
In any case, I just don't think this is going to work for me. Hopefully the 'plug and play' nature of the DATS box will be easier to manage.
Thanks again for your help.

To answer some of your questions, in case any of this helps someone else in the future...
I'm using this external card from Amazon: https://smile.amazon.com/gp/product/B076PC4VV4
It supposedly has a stereo Mic input, and line-in as well, which is why I bought that one.
It uses USB to interface with the computer, and all 1/8" (3.5mm) for the rest of the connections.
My laptop has separate headphone out and mic input jacks, both 3.5mm. I know you say that a mic jack isn't suitable, but I've seen it working on the video in the OP, so I know it's possible.
I'm using all stereo jacks, but the output (I think, could be the input) jack is wired only to one channel, making it effectively mono, as shown in the diagram you posted earlier.
I obviously didn't know anything about the signal gen, so I haven't tested that, but I can say that on the external card, when there are no signal inputs, the level is at about -32dB, which I find very suspicious.
 

John Mulcahy

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My wife finally saw my frustration last night and pulled the plug, by which I mean she bought me the Dayton DATS box.
Very good of her!
I can say that on the external card, when there are no signal inputs, the level is at about -32dB, which I find very suspicious.
Sounds broken.
 

Elmojo

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She's a good one for sure! :)
I agree, I think the external sound card has issues.
That doesn't explain, though, why I get similar whack-o results from the internal card on the laptop, and the Audigy 5/RX card in my desktop machine.
 
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