Suggestion: more audio interface measurements

[Blumlein 88]

Here are some examples
EIN (A weighted) with 150 ohm resistor, 20Hz-20kHz

View attachment 227535

But I think the Dynamic range plot is more "readable"
As an example you see more clearly what the AD8HR is doing.

View attachment 227536

The important thing, in my opinion, is to align "gains" in a meaningful way.

And the only meaningful way is: "I have that mic that gives me that Voltage max for my use case. I want to compare all mic preamps with a gain that is the max gain allowing not to saturate my preamp or ADC with that voltage."
(I decided a threshold THD of 0.1%, but saturation is usually very brutal, so this threshold value doesn't matter much)

Here above, my "reference gain" (0dB) is the max gain to allow 100mV rms input.
(That's about the max level you'll get from a Shure SM58 with a singer in real life)
That's 35dB on the RME (max ADC level at 0dB gain marking = 18dBu) and 44.2dB on the Millenna (45dB gain marking - max output before saturation 27dBu)
For the Yamaha, it's -37dB gain marking (max ADC level for 0dB gain marking is 20dBu).

NB: For fun, I added the RME ADI-2 Pro fs R for its 4 input ranges.
Of course, it can't act as a mic preamp. For this kind of level, you'll need a condenser microphone, that requires a phantom power, and the ADI-2 doesn't have one.
Still, you understand here why you can't get better measurements from the UCX II for mid level signals.


You learn from the above what really makes the difference between an high end mic preamp and a cheaper -but still excellent- one:
The gap is big for LOW gains.
So use in priority such a preamp with high level output microphones (Condenser) or sources (drum kit).

You also realize that it is more meaningful to measure EIN (A) at 30dB gain than at 60dB gain...

Yes, most pre's have better EIN at higher gain. How much makes sense to test is more variable. The big thing being condenser micrphones or dynamics and ribbons. I've measured a handful of devices and some lose little EIN down to 20 db gain or less and some lose quite a lot of EIN below or at 40 db. Some that seem good at lower input levels won't take high levels you get with some condensers. So you do want to know where the overload input level lies.

 

[signalpath]

Well, it's not that simple.

For my plots above, you have to first measure accurately the gain of your preamp for each gain marking (for an analog preamp) or the ADC level variation from gain to gain.
You also have to check at what level it will saturate (if any) for each gain.
Then you have to measure noise with your resistor (that's the easy part).

But, ideally, you also have to compensate for you actual resistor value vs 150 ohm and for the temperature.

All this is a lot of manipulations.
Worse: On some old mixers I have, you can't set the gain knob to the exact same value twice.
So, you'll have to do all the above for each gain then move to the next value.
Which means a lot more cable changes.
Quite a lengthy process...



Actually, it doesn't matter, as long as we agree on ONE input level to align all gains around it.
I plan to do a "dashboard" for mic preamp at 3 gain settings:
Gain for 100mV max, for 1V max and for 10mV max.
Each measurement at an input level to get -10dBFS.

Here is an example
(You may find more in the posts of the thread here)

RJA, over the next few years, I predict we will see paradigm-shifting breakthroughs in micamp, ADC, DAC, and power amp objective performance. Perhaps >30dB improvements in dynamic range, linearity, low-level THD, and baseline noise. This performance shift will likely start with D-A circuits.

 

[Trell]

RJA, over the next few years, I predict we will see paradigm-shifting breakthroughs in micamp, ADC, DAC, and power amp objective performance. Perhaps >30dB improvements in dynamic range, linearity, low-level THD, and baseline noise. This performance shift will likely start with D-A circuits.

Not sure if I understood you correctly but we already have devices that measures excellently, and if you look at the reviews here on ASR I’ve a hard time believing a 30+ dB improvement. Perhaps you meant for the lower tier?

 

[Rja4000]

Not sure if I understood you correctly but we already have devices that measures excellently, and if you look at the reviews here on ASR I’ve a hard time believing a 30+ dB improvement. Perhaps you meant for the lower tier?

I doubt the founder of Millennia Media (aka signalpath) speaks about lower tier ;-)

 

[Rja4000]

RJA, over the next few years, I predict we will see paradigm-shifting breakthroughs in micamp, ADC, DAC, and power amp objective performance. Perhaps >30dB improvements in dynamic range, linearity, low-level THD, and baseline noise. This performance shift will likely start with D-A circuits.

Thanks for your input.
To reach this kind of improvement, I suppose you'd need to combine several gains or DAC/ADC ranges ?

 

[signalpath]

Thanks for your input.
To reach this kind of improvement, I suppose you'd need to combine several gains or DAC/ADC ranges ?

Precisely! The next audio frontier is multi-path (multi-range) topology.
It's not a new idea. Here's a 2012 Analog Devices patent for a multi-path microphone.

https://patentimages.storage.googleapis.com/3e/8d/20/b27e912bdb8375/US8223981.pdf

 

[Philbo King]

It might be an interesting challenge to automate the more tedious tests, such as worst case crosstalk from each channel to all other channels, FR for each channel, bell and HP/LP shape for EQs on each channel and how much it varies from channel to channel, etc.

It would take an electronically switched patchbay (so you could hook up every input and output at once), a batch-test facility in REW, all controlled by a PC program that would control the patchbay and REW. Or something equivalent.

I used to design stuff like that and write control software for automated test systems for avionics & aerospace 'boxes'.

We even had an in-house programming language dedicated exclusively for running automated test racks, called ADATE. I'm sure the name was from an acronym, but I remember it as "Another Damned Acronym To Explain".

Just doing a bit of dreaming... The test systems were sold to airlines and service centers for north of 1.5 million bucks. Considering there were often multiple thousands of inputs and outputs that had to be tested in a given box, it was a bargain. But surely little rich for a hobby website...

 

[Rja4000]

"Another Damned Acronym To Explain".

IHT(f)A *




* I Hate Those (f...) Acronyms
(copyrighted under my name)