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Behringer Monitor1 tests

DavidR

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Aug 19, 2024
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Given the price and how I planned to use it, I bought a Monitor1 after reading some the discussion in threads here. My planned use is a different story (probably moot now), so I'll cut to the chase. I've been testing the Focusrite Scarlett 2i2 that will be paired with the Fosi V3 Mono for use in amp and (primarily) speaker testing. I wanted to test and characterize them for a baseline. The Scarlett is covered in other threads, not needed here other than reference. What bothers me is the Monitor1. It's cheap, yeah, though it looks and feels like decent quality. It's only a passive attenuator, not a real pre-amp, so I expected typical attenuation without much else, maybe a bit of additional distortion. It hasn't turned out that way.

There's a focus on distortion in so many threads here that seem to have overlooked one aspect. Either that or I just didn't find a thread on what to me is #1, bandwidth linearity. #2 is distortion, but I expected a passive attenuator to be close to benign. After all it's only connectors, a few short conductors and in this case a single, stereo balanced pot. But unless I've done something wrong (don't see how, it's just balanced cabling), the Monitor1 is a disappointment.

I've got a few REW measurements to post. These will be just the Scarlett loopback or the Scarlett with the Monitor1 in the loopback. I eventually made a cal file of the Scarlett loopback with the Monitor1 in the loop, but not until after a number of distortion tests.
 
This is an overlay of a Scarlett 2i2 loopback RTA over a Scarlett-Behringer Monitor1 loopback RTA. The generator setting is close to what seems to be optimal for the Scarlett due to the input. All tests were run with the Scarlett dials set for maximum output and no input gain. Note that all Scarlett distortion harmonics (green) are in or below the noise. The Monitor1 in the loopback adds up to 10dB more noise. The connections are all balanced interconnects only, nothing else.
RTA Frequency Overlay Scarlett -25dBFS Behringer Monitor1 Max.jpg


Edit: I forgot to say that it's the 2i2 Gen 4.
 
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With passive attenuation you do need to keep cables on the output of the attenuator short and of low capacitance not to roll off the treble. Distortion should not be an issue unless the input impedance is too low for the source. The Monitor 1 is 10 kohm input impedance so shouldn't be a problem. I do note their specs list THD as .01% which honestly seems high for such a device, but shouldn't be audible. It is in line with what you are showing. Also note that the increased output impedance by itself will raise the noise floor enough to measure. Other than more distortion than I would expect it looks about like it should in your measurements. The distortion is in line with the specs from Behringer. It isn't enough you will hear it.
 
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I ran various tests and eventually settled on those that follow that I think detail it best, all using REW through the Scarlett 2i2. I was puzzled by various distortion tests, This set compares the THD and harmonic components up to H5 of the Scarlett 2i2 alone at its optimal generator output, the Scarlett-Behringer at the same output and the Scarlett-Behringer at a higher generator output. That output was determined by measuring the voltage at the Scarlett input for its optimal (-25dBFS) that was 0.281V. I put the Behringer back in and increased the gen output until the loopback from the Monitor1 matched. That required a gen output of -13.3dBFS. This will lead to another post later.

Scarlett 2i2 Loopback with Behringer Monitor1 Distortion.jpg


What really surprised me is how the Behringer adds significant distortion for THD, H2 and H3, but has decreasing addition of the higher harmonics. H2 and H3 are seriously higher. These were all generated using the RTA Swept sine at 1kHz.
 
What I find most disappointing is the bandwidth linearity. This is a calibration using REW of the Scarlett-Behringer.

Edit: using 2m cables

Scarlett 2i2-Behringer Monitor1 Calibrtion 48kHz Sample Rate.jpg
 
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Finally this is a set of calibrations using two settings for the Monitor1 gain with one also at higher generator setting. Incidentally, when the Monitor1 is set to maximum (all previous tests were made at its maximum), the is significant voltage drop. All other passive attenuators I've ever had passed close to 100% of the input voltage. Not so the Monitor1 unless I have a lemon. Also, the output voltage does not change at all from 100 down to 90.

S-THD vs Frequency Overlay Various Levels.jpg
 
The balanced loopback cables I have when using the Monitor1 are 2m. This shouldn't be considered long in my opinion since they are balanced. I can't vouch for the impedance. When I return home next week I'll run calibration on the Scarlett alone with 2m cables to compare.
 
Both the voltage drop and harmonic distortion are subject to damping factor, so results depend significantly on the output- and input impedance of your test equipment.

I'd even wager that that's all that you're seeing really: high voltage drop and increased H2 because the poor Scarlett is struggling to drive a somewhat challenging load.
 
I just saw a more recent post on the 2i2 with more testing that indicates a very different optimal point. Next week I'll do more testing to see if my tests should be modified. I determined what I called optimal by making pure loopback tests of the 2i2 using REW. I chose the point of lowest distortion.
 
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I just saw a more recent post on the 2i2 with more testing that indicates a very different optimal point. Next week I'll do more testing to see if my tests should be modified. I determined what I called optimal by making pure loopback tests of the 2i2 using REW.
When the Monitor1 is set to maximum output the loopback of the Scarlett 60k input in parallel with the 10k Behringer. Seems to me that the Scarlett ought to be capable of driving that.
 
When the Monitor1 is set to maximum output the loopback of the Scarlett 60k input in parallel with the 10k Behringer. Seems to me that the Scarlett ought to be capable of driving that.
Well it would see 10k at the Monitor 1. I agree if the Scarlett cannot handle that something is amiss.
 
If I could find a decent panel-mount balanced attenuator to wire in and replace that board-mount one I'd be tempted. For the distortion aspect I wonder how much has to do with the layout of the circuit board or the soldering. My guess, though, is that the problem is the quality of that attenuator. Given that I have no need of the mono nor mute switching would it be worth replacing the entire circuit board with a better attenuator and keep the sockets?
 
I can see why you might want it better. OTOH, if it is for speaker testing, nothing it is doing will be an issue. Well actually the unflat frequency response would be. I'm not sure I see how the volume pot is doing that. 2 meters is not enough, for that I don't think. As a check either use longer or shorter cables at the output by a factor of at least 2x and see how the frequency response changes. That will tell you if it is simply output impedance interactions with the cable.
 
I found the problem and it wasn't hardware. I have left REW up and running continuously for some time. I have an old laptop that I don't close because I have REW and other apps running to leave as they are. Yesterday I tried the right channel on the Monitor1, but the response was strangely erratic, I thought I had a lemon. Went back to the left channel, same thing. So I re-started REW. That totally cleared the problem. I had seen REW to have small issues in the past, but maybe it has an occasional issue with its internal buffers. In any case, the Monitor1 now responds exactly as I had first expected. I'll post some new graphs to demonstrate. I sure lost a lot of time fighting what what appears to be a software bug.
 
This is an REW calibration run comparison of the Scarlett 2i2 alone and a calibration run with the Behringer Monitor1 in the loopback. The Monitor1 was set at 100 (maximum on the dial). I am still a bit surprised at the drop in level when the Monitor1 is at its maximum setting, but at least the drop is uniform across the spectrum.

Edit: I measured the voltage at the Scarlett input again without then with the Monitor1 in the loop. The difference is not minor. The issue with REW that required a distinctly different generator output to match the two is now almost nil.
Scarlett 2i2 cal vs  Behringer Monitor1 in Loopback cal.jpg

This is an overlay of stepped THD loopback of the Scarlett alone (red), Monitor1 at 100 (black) and Monitor1 at 80 (blue). The REW generator was set to -25dBFS that is close to the optimum for the Scarlett when using its generator for signal. Note that it can't max out the Scarlett input, so the graph ends at 0dBFS (generator graph selection). The Monitor1 at 100 has small amount of harmonics showing higher than the Scarlett alone, but insignificant. The Monitor1 at 80, however, shows significant increase in harmonics, but still acceptable.
Scarlett 2i2 Loopback Through Behringer Monitor1 - RTA HD vs Frequency.jpg

This is the RTA THD graph of the Monitor1 at 80 in the Scarlett loopback that shows the harmonic breakdown.
RTA HD vs Frequency Behringer Monitor1 at 80.jpg
 
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Here are a few graphs of the Stepped-THD results of the Scarlett 2i2 loopback with the Behringer Monitor1 in the loopback. The REW generator was at -25dBFS again with the Monitor1 at various level settings.
S-THD vs Level Scarlett 2i2 through Behringer Monitor1 Various Monitor1 Level Settings - THD.jpg

S-THD vs Level Scarlett 2i2 through Behringer Monitor1 Various Monitor1 Level Settings - H2.jpg

S-THD vs Level Scarlett 2i2 through Behringer Monitor1 Various Monitor1 Level Settings - H3.jpg

S-THD vs Level Scarlett 2i2 through Behringer Monitor1 Various Monitor1 Level Settings - H4.jpg

S-THD vs Level Scarlett 2i2 through Behringer Monitor1 Various Monitor1 Level Settings - H5.jpg

I would expect the distortions to rise at the lower Monitor1 levels since noise will remain the same, but the its doesn't have a change in output level until the dial is below 90. That I find strange. At the maximum setting the output should be almost the same as without it in the circuit, but as show in post 16 above the Monitor1 output is about 0.2dB below the Scarlett itself. There is little change in the distortion profile at Monitor1 maximum, however, seen in post 16.
 
Now that the issue with the earlier measurements has been solved, I'm impressed with this passive attenuator that sells at such a low price. O have not tested the channel balance, by my need is for a single channel. I may compare them as an academic exercise from curiosity.
 
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I use the Monitor1 in my measurements sometimes and it's adding no distortion by itself (unless you really push the level too high).
It's for me the best way to keep noise level low while adjusting freely the level down.
Note that I have 2 of them, and they perform slightly differently. I selected the channel with best results.
 
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