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PreSonus Quantum measurements?

buxtehude

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With recent audio interface reviews published by amirm, I got curious how Presonus Quantum measures and ranks against other interfaces.
Any info on these? Especially Main line outputs and Headphone Outputs.

Quantum
presonus-quantum-front_big.jpg

presonus-quantum-back_big.jpg


Quantum2
presonus-quantum_2-front_big.jpg

presonus-quantum_2-back_big.jpg


https://www.presonus.com/products/quantum
https://www.presonus.com/products/Quantum-2
 

AnalogSteph

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I mean, it's Presonus, their engineering isn't always the best. I wonder how the Quantum managed to get such a lot of jitter in loopback, I can only assume that D/A and A/D clocks are generated by independent PLLs that aren't the last word in phase noise.

Quantum 2626 performance is more in line with the converter and opamp complement, decent midrange level times a bunch of channels - considering it's by far the cheapest Thunderbolt interface with 8 mic inputs stocked at Thomann, there isn't too much to complain about.
 

Morgoth

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I bought the larger Quantum unit a few years back. They're good for the intended use case, being extremely low latency so you can get really great real time tracking through your DAW without needing to set the buffer size to 32 samples, which puts waaaaay too much stress on the CPU (I think I was usually able to keep it at 128 samples and still had super low latency). I originally bought it for live shows, and can't complain about it's performance in that application. It has plenty of digital I/O to bypass the converters, so you can essentially just use it as a low latency bare bones interface, with outboard preamps and converters. In fact, I gave away this interface to my old guitarist, and he's using external converters, headphone amp, and preamps with it. He runs instances of Neural Dsp plugins through Logic X, and he's sensitive to anything above a reported 3-4ms round trip latency when tracking, so this seems to do the job for him.
 
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buxtehude

buxtehude

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I bought the larger Quantum unit a few years back. They're good for the intended use case, being extremely low latency so you can get really great real time tracking through your DAW without needing to set the buffer size to 32 samples, which puts waaaaay too much stress on the CPU (I think I was usually able to keep it at 128 samples and still had super low latency). I originally bought it for live shows, and can't complain about it's performance in that application. It has plenty of digital I/O to bypass the converters, so you can essentially just use it as a low latency bare bones interface, with outboard preamps and converters. In fact, I gave away this interface to my old guitarist, and he's using external converters, headphone amp, and preamps with it. He runs instances of Neural Dsp plugins through Logic X, and he's sensitive to anything above a reported 3-4ms round trip latency when tracking, so this seems to do the job for him.

Extremely low latency is the reason I got it as well. Worked well for my use case. And I was pretty satisfied with it until I read those measurements. (I am starting to think looking at these measurements are not good for my mind... haha) Also the Spdif out worked well with my Genelec 8330 GLM's AES input, (with impedance transformer of course...) For my needs, low latency trumps everything else and even to this date, not many can match Quantum in terms of latency, definitely a keeper for me.
 

vertumno

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Well... That's pretty not great!
Hello,
Could you (or anyone) possibly expand on that comment?

I've read the review (translated) and it only says great things about it, but I've probably missed something in the measurements?

I have a Quantum and I have my own reservations, especially about reliability and support.

Thank you!
 

AnalogSteph

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It's mostly this:

thd.png

compared to this:
dynamics.png


See how much the noise floor is rising around the 1 kHz tone at high level? Clearly somebody's clock has a bit of a jitter problem. Which is odd given that you'd think things like that should cancel in loopback. I wonder which side is the problem, D/A or A/D? Distortion is a bit so-so as well. The nominally lesser 2626 actually is much better-behaved overall. You'd expect the big one to measure at least as good or even better, not worse.

Now can you hear that? No, I don't think so, instantaneous dynamic range should still come out to greater than 16-bit level like that. It's just obviously mediocre from an engineering POV when it wouldn't have to be. I'm sure when you're out developing audio interfaces there'll be the odd Audio Precision or similar floating around in the lab. Even a simple loopback test would have exposed the issue. Who knows, maybe they were on a deadline or something and didn't have time to hunt this down.
 
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buxtehude

buxtehude

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It's mostly this:

thd.png

compared to this:
dynamics.png


See how much the noise floor is rising around the 1 kHz tone at high level? Clearly somebody's clock has a bit of a jitter problem. Which is odd given that you'd think things like that should cancel in loopback. I wonder which side is the problem, D/A or A/D? Distortion is a bit so-so as well. The nominally lesser 2626 actually is much better-behaved overall. You'd expect the big one to measure at least as good or even better, not worse.

Now can you hear that? No, I don't think so, instantaneous dynamic range should still come out to greater than 16-bit level like that. It's just obviously mediocre from an engineering POV when it wouldn't have to be. I'm sure when you're out developing audio interfaces there'll be the odd Audio Precision or similar floating around in the lab. Even a simple loopback test would have exposed the issue. Who knows, maybe they were on a deadline or something and didn't have time to hunt this down.

Thank you so much for the detailed explanation! I have a dumb question. If I keep everything digital, is my signal still affected by the issue you mentioned above? Let's say
  • I am playing 16bit 44.1kHz WAV file from MacBook Pro
  • Quantum 2 connected to MacBook Pro via Thunderbolt 2.
  • Quantum 2's SPDIF out connected to Genelec 8330's AES/EBU input
In this case, am I still being affected by the issue you pointed out above?
 

vertumno

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It's mostly this:
Thank you, much appreciated.
My experience with the Quantum (the smaller Quantum 2 actually, but the innards should be the same) has been a bit erratic, so I'm gathering more specific info than the audio magazines reviews.
 
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AnalogSteph

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Quantum 2 is another different device altogether, so I wouldn't count on measurements for one applying to the other. In a moderately complex device like this there is quite a bit room for quirks for sure (including drivers and system interoperability).

  • Quantum 2's SPDIF out connected to Genelec 8330's AES/EBU input
In this case, am I still being affected by the issue you pointed out above?
That would depend on the jitter rejection (PLL bandwidth) of the Genelecs' SPDIF receiver... But again, Quantum 2 != Quantum.
 
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buxtehude

buxtehude

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Quantum 2 is another different device altogether, so I wouldn't count on measurements for one applying to the other. In a moderately complex device like this there is quite a bit room for quirks for sure (including drivers and system interoperability).


That would depend on the jitter rejection (PLL bandwidth) of the Genelecs' SPDIF receiver... But again, Quantum 2 != Quantum.

I see. Thanks again @AnalogSteph
 

vertumno

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Quantum 2 is another different device altogether, so I wouldn't count on measurements for one applying to the other. In a moderately complex device like this there is quite a bit room for quirks for sure (including drivers and system interoperability).


That would depend on the jitter rejection (PLL bandwidth) of the Genelecs' SPDIF receiver... But again, Quantum 2 != Quantum.

I get what your saying, there might be quirks.
However if you trust their respective tech sheets measurements they seem to show identical readings. It might be fair to assume that their performance is nearly identical too, don’t you think?
Unless presonus just copied and pasted readings from Quantum to Quantum 2.
 

AnalogSteph

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If you want, you could do some loopback testing.
RMAA 6.4.5 test signals: 24/44, 24/48, 24/96, 24/192
Play calibration signal in a loop, bit-perfect, at full output and adjust input gain for about -1 dBFS peak undistorted. Record at same sample rate (use a software playthrough function if need be). Latency is not critical, make sure there are no drops. Upload recording somewhere for someone's RMAA to chew on it.
 

vertumno

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If you want, you could do some loopback testing.
RMAA 6.4.5 test signals: 24/44, 24/48, 24/96, 24/192
Play calibration signal in a loop, bit-perfect, at full output and adjust input gain for about -1 dBFS peak undistorted. Record at same sample rate (use a software playthrough function if need be). Latency is not critical, make sure there are no drops. Upload recording somewhere for someone's RMAA to chew on it.
Thanks for the tips, It’d be very interesting but I’ve never done this kind of procedure and I’m not sure it’d be a reliable tester.
 

Grooved

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Thanks for the tips, It’d be very interesting but I’ve never done this kind of procedure and I’m not sure it’d be a reliable tester.

It can give some elements to compare with other interfaces.
One test has been done on the Quantum with the GS loopback test, also processed in Deltawave by Pkane (https://deltaw.org/gearslutz.html#)
Results (lower is better) :
GS RMS (L) / DW RMS(dBFS) / DW RMSEQ(dBFS) / DW RMSEQ(dBA) / DW PK Metric (dBFS)
-45.2 / -45.1 / -70.1 / -70.6 / -75.5

With a 18 years old 828 MKII (I have other RME, Universal Audio,... interfaces to test when I will get enough time), this is what I get (the value in the link above for the 828 MKII is wrong as test was done in unbalanced mode, I did it in balanced mode) :
-56.7 / -56.7 / -90.7 / -101.2 / -108.2

The best results come from the RME ADI-2 Pro in "Sharp" mode
-53.9 / -53.8 / -91.4 / -111.1 / -116.2

This would say that the Quatum is far from optmized
 

vertumno

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It can give some elements to compare with other interfaces.
One test has been done on the Quantum with the GS loopback test, also processed in Deltawave by Pkane (https://deltaw.org/gearslutz.html#)
Results (lower is better) :
GS RMS (L) / DW RMS(dBFS) / DW RMSEQ(dBFS) / DW RMSEQ(dBA) / DW PK Metric (dBFS)
-45.2 / -45.1 / -70.1 / -70.6 / -75.5

With a 18 years old 828 MKII (I have other RME, Universal Audio,... interfaces to test when I will get enough time), this is what I get (the value in the link above for the 828 MKII is wrong as test was done in unbalanced mode, I did it in balanced mode) :
-56.7 / -56.7 / -90.7 / -101.2 / -108.2

The best results come from the RME ADI-2 Pro in "Sharp" mode
-53.9 / -53.8 / -91.4 / -111.1 / -116.2

This would say that the Quatum is far from optmized

Thank you!

Would be interesting to see other RMEs, I have a FF400 alongside the Quantum2
 

Grooved

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Thank you!

Would be interesting to see other RMEs, I have a FF400 alongside the Quantum2
The results on the Deltawave website are done with a automatic script and Deltawave measures using the audio files submitted on Gearspace, so I think that Pkane will run it once more added on Gearspace.
The FF400 is not in the test, there's only the FF800 getting -44.1 / -42.6 / -81.6 / -86.3 / -92.6

Now, there are not both working the same way :
- the FF800 has two different chips doing DA and AD : AK5385 and AK4395/AK4396
- the FF400 has one kind of chips doing both DA and AD : AK4620A (and on some MOTU devices, it works really good with the AK4528)
 
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