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Author Topic: Measurement Interfaces  (Read 9453 times)

Scott Carneval

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Re: Measurement Interfaces
« Reply #10 on: October 04, 2016, 02:00:54 pm »

I've been using the SMAART I/O for several years, but I've recently started using my Behringer XR18 for multi-channel measurements. I was looking for a new interface when it dawned on me that the Behringer essentially IS an 18ch USB interface. It actually saves a piece of gear because it's my mixer and interface all in one.
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Mark McFarlane

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Re: Measurement Interfaces
« Reply #11 on: March 02, 2017, 11:46:43 pm »

I know I will get some flack for this, but here is a interface that simply works.

No software-no drivers.

Just plug it in and the software will see it.  Select "device" and you are good to go.

The price is right-so if you lose it-no big deal.

The cheaper one is the Behringer UMC202.  If you want balanced outputs and more inputs the UMC404.

I have been playing around with it for a little while and am pleased.

Every now and then there is a "diamond in the rough".


Ivan, regarding SMAART interfaces, the UMC404 has been replaced by a newer version UMC404HD. Pretty cheap at $99 for 4 mic preamps and the XLR outs are a bonus.  It has global phantom.


Have you ever had a problem with global phantom and looping back your reference from/to your UMC202?  I had a problem years ago with an Edirol interface where the phantom power messed up the loopback signal.


Lately I've been using my GLD as a SMAART interface, but I'm starting to work on other people's systems more frequently and need at least 4 portable channels. $99 is pretty much a no-brainer investment.
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Mark McFarlane
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Nathan Riddle

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Re: Measurement Interfaces
« Reply #12 on: March 03, 2017, 10:47:47 am »


Ivan, regarding SMAART interfaces, the UMC404 has been replaced by a newer version UMC404HD. Pretty cheap at $99 for 4 mic preamps and the XLR outs are a bonus.  It has global phantom.


Have you ever had a problem with global phantom and looping back your reference from/to your UMC202?  I had a problem years ago with an Edirol interface where the phantom power messed up the loopback signal.


Lately I've been using my GLD as a SMAART interface, but I'm starting to work on other people's systems more frequently and need at least 4 portable channels. $99 is pretty much a no-brainer investment.

I thought it was just a bad idea period to run phantom into an output. I use the an XLR-F to TRS-M for the reference signal.
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Mark McFarlane

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Re: Measurement Interfaces
« Reply #13 on: March 04, 2017, 02:33:00 pm »

I thought it was just a bad idea period to run phantom into an output. I use the an XLR-F to TRS-M for the reference signal.


You are correct. I think I didn't have the right cable,... it was a decade ago.
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Keith Broughton

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Re: Measurement Interfaces
« Reply #14 on: March 04, 2017, 03:05:37 pm »


Ivan, regarding SMAART interfaces, the UMC404 has been replaced by a newer version UMC404HD. Pretty cheap at $99 for 4 mic preamps and the XLR outs are a bonus.  It has global phantom.


Have you ever had a problem with global phantom and looping back your reference from/to your UMC202?  I had a problem years ago with an Edirol interface where the phantom power messed up the loopback signal.


Lately I've been using my GLD as a SMAART interface, but I'm starting to work on other people's systems more frequently and need at least 4 portable channels. $99 is pretty much a no-brainer investment.
I use the 404HD and take a TRS from out 4 (set as test out) and loop it back (TRS) to input 4.
This gives 1-3 mic channels with phantom for measurements and channel 4 is reference.
No issue with phantom on TRS inputs.
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Ivan Beaver

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Re: Measurement Interfaces
« Reply #15 on: March 04, 2017, 03:55:26 pm »


Ivan, regarding SMAART interfaces, the UMC404 has been replaced by a newer version UMC404HD. Pretty cheap at $99 for 4 mic preamps and the XLR outs are a bonus.  It has global phantom.


Have you ever had a problem with global phantom and looping back your reference from/to your UMC202?  I had a problem years ago with an Edirol interface where the phantom power messed up the loopback signal.


Lately I've been using my GLD as a SMAART interface, but I'm starting to work on other people's systems more frequently and need at least 4 portable channels. $99 is pretty much a no-brainer investment.
My standard cable that I use for dual transfer functions has a TRS on one end-but only hooked up to the T and S.

There are 2 cables that come out of the connector.
The connector plugs into the headphone output.

One is a TRS-with the hot to tip and the shield to R (no connection to shield)
This goes to the TRS input of the reference channel

The other cable is a MXLR that has the tip hooked to pin2 and the shield hooked to pin 3.

This allows me to vary the SPL out of the loudspeaker, without affecting the signal displayed-since both the reference and measurement go up and down at the same time.

It is also REAL good for looking at power compression of drivers in real time.
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Langston Holland

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Re: Measurement Interfaces
« Reply #16 on: August 18, 2018, 09:44:12 pm »

Hello fellow cheapskates*:

I thought this would be of interest. :)

Advertisements for the Focusrite Scarlett 2i2 Gen 2 claim it to be the best selling audio interface of its type in the world. Given its low price, good looks, massive advertising budget and great specs (except the ones they don't mention), I can see why.

Summary

Buy this thing if you use Smaart or SysTune.

It is a great USB bus powered choice for dual channel FFT measurement at 96k sample rates and below. It's output noise at higher sample rates is so bad that they shouldn't have enabled it. Input is very quiet but I still would never consider this unit for what it's advertised for (recording) because of its poor phase performance. The time domain error is the same on each channel, thus cancels out with the magic of dual channel FFT. With recording it does not cancel - it's permanently embedded in your tracks.

If Focusrite fixed the phase error on the input channels this thing would be the steal of the century for home studio tracking and even more serious stuff. My speculation is that they compromised phase in order to reduce latency as is done with digital wireless. Low latency is a big deal for monitoring during recording.

Odds and Ends

Measurement gizmos used were the Audio Precision APx515, FIR Capture, Keysight U1282A and U1733C. The Focusrite Windows ASIO driver is solid as a rock. The APx515 allows you to send or receive from a DUT through ASIO, thus allowing closed loop measurement of the analog inputs and outputs independently.

Phantom power is excellent, 47.6V unloaded and 14.3V when both channels have full 10mA loads. The outputs are unaffected by the presence of phantom power. XL input impedance is 3,025Ω from 100Hz to 10kHz, sloping down to 2,115Ω at 100kHz. This impedance is the same with or without phantom power engaged. Construction is above average disposal class; you probably have to pry off the back panel to get at the screws. Input signal and clip indicators are nicely visible, cool looking and accurate.

Measurements

This unit has analog gain adjustments for both input and output, thus you should adjust both so that you can keep the digital signal as close to full scale as possible. I chose -3dBFS for these measurements. The mfg specs use -1dBFS, which isn't safely achievable in use.

Flat lines from a dual channel FFT measurement program called FIR Capture at each of the tested sample rates:



Phase input and output:





Magnitude input and output:





Noise input and output:





Distortion at -3dBFS:













And my Pin 1 torture test. Very few gizmos have passed it:





*A cheapskate is a semisentient being that spends twice as much money at four times the grief as the buy-once, cry-once heretic.
« Last Edit: August 18, 2018, 09:59:11 pm by Langston Holland »
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David Sturzenbecher

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Re: Measurement Interfaces
« Reply #17 on: August 18, 2018, 10:55:41 pm »

Hello fellow cheapskates*:

I thought this would be of interest. :)

*A cheapskate is a semisentient being that spends twice as much money at four times the grief as the buy-once, cry-once heretic

Thank you for the analysis Langston!  My Scarlett 2i2 went belly up just a week or so ago. Initial observations see a bulging-open bottom electrolytic cap on the PCB. The device was great to throw in the backpack when octacapture was overkill. Still debating if it's worth tracking down the specific capacitor, and troubleshoot if there are other issues.



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Langston Holland

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Re: Measurement Interfaces
« Reply #18 on: August 18, 2018, 11:46:41 pm »

Quote
Initial observations see a bulging-open bottom electrolytic cap on the PCB...

Hi David:

How did you take it apart? Is it just an issue of prying off the rear panel?

Don't bother if it isn't easy, but a picture of the internals would be fun. :)

Edit: Skip it - sorry I didn't think about YouTube. (2) Screws under the rear rubber feet and you're in like Flynn. :)
« Last Edit: August 19, 2018, 12:25:30 am by Langston Holland »
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Nathan Riddle

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Re: Measurement Interfaces
« Reply #19 on: August 19, 2018, 02:44:48 pm »

Hello fellow cheapskates*:

Advertisements for the Focusrite Scarlett 2i2 Gen 2 claim it to be the best selling audio interface of its type in the world. Given its low price, good looks, massive advertising budget and great specs (except the ones they don't mention), I can see why.

Langston,

I have a first gen 2i2 sitting on my desk that I've been using to take measurements, I wonder how they compare?

I am a short drive away, maybe we can meet up sometime?
I love this geek-out/test-n-review stuff you do!
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