Audio Interface Suitable for Measurements

[sergeauckland]

I eliminated the UMC202/4HD on loopback, where the distortion was around 1.2% at 1kHz with the input kept below clipping. This was substantially the same whether balanced in/out, unbalanced in/out or mixed balanced to unbalanced. The DAC part was better than the ADC, but I still couldn't get the DAC to measure near what the spec was, using tones generated by Audacity or other software tone generators. My very cheap UCA202 did a lot better as a DAC.

S

 

[RayDunzl]

The Clarett series is supposed to be the same mostly as the Forte and they currently sale it and it will get software support better than the Forte.

Ordered a Clarett 4pre.

 

[Earfonia]

Ordered a Clarett 4pre.

I would be interested to see the measurement result of the Clarett 4pre

 

[JohnYang1997]

clarett 4pre can give 0.00008% thd no n at around -20dbFS.

 

[RayDunzl]

I would be interested to see the measurement result of the Clarett 4pre

Sending via USB on channel 1 with a cheap blanaced TRS on output ch1 looped back to front input ch3 XLR at 96kHz

The output knob of ch1 and the input knob of ch3 are at about the half point of their range.

A hint of 2nd harmonic at the level of -6dBfs

At -3dBfs the 2nd is a little stronger and something shows up near nyquist:

At -1dBfs a little more 2nd and much more HF stuff (the HF stuff is not the generator).

At -0.5dBfs the lower harmonics pop up.

There you go.

 

[JohnYang1997]

Sending via USB on channel 1 with a cheap blanaced TRS on output ch1 looped back to front input ch3 XLR at 96kHz

The output knob of ch1 and the input knob of ch3 are at about the half point of their range.

A hint of 2nd harmonic at the level of -6dBfs

View attachment 29998

At -3dBfs the 2nd is a little stronger and something shows up near ntquist:

View attachment 29999

At -1dBfs a little more 2nd and much more HF stuff

View attachment 30000

At -0.5dBfs the lower harmonics pop up.

View attachment 30003

There you go.

Very nice.

 

[Earfonia]

Sending via USB on channel 1 with a cheap blanaced TRS on output ch1 looped back to front input ch3 XLR at 96kHz

There you go.

Many thanks!
Looks like the Clarett 4pre is pretty clean to be used for measurement. What do you think?

 

[helloworld]

Many thanks!
Looks like the Clarett 4pre is pretty clean to be used for measurement. What do you think?

The noise is kind of large.....

 

[RayDunzl]

The noise is kind of large.....

Compared to what?

 

[helloworld]

Compared to what?

motu ultralite mk4 in page one

 

[Interference]

Provided that without calibrating the input it's hard to draw conclusions, a -92 dbFS noise floor looks pretty mediocre for an interface on this range. You should test the input at minimum gain. Clarett 4Pre RMAA results show around 110 dB of dynamic range in loopback, decent but not as good as Clarett 2Pre (and I guess still a bit short of the good ol' E-MU 0404).

 

[JohnYang1997]

The noise is kind of large.....

Don't look at noise floor in fft spectrum. It's meaningless.

 

[Earfonia]

A quick loopback test on XLR Output and Input of the RME Babyface Pro at various level (PAD ON):


Output level 0 dBFS and 0 dB input gain:

Output level -3 dBFS and 0 dB input gain:

Output level -6 dBFS and 0 dB input gain:

Quick RMAA test at 0 dBFS output and 0 dB input gain:

I saw some REW screenshots here that shows the DR (Dynamic Range) value on the RTA Window, which setting do I need to enable to show the DR value?

I also couldn't set the REW generator to 0 dBFS, only -3 dBFS, any setting to enable the 0 dBFS on the function generator? Thanks!

 

[JohnPM]

You need the latest beta version for a Noise+Distortion figure, which should be measured at -60 dBFS and combined with the max level to provide a DR figure. The "DR" figure was based on an assumption of -0.1 dBFS max level, it has been retired. To have the generator allow up to 0 dBFS select the "Full scale sine rms is 0 DBFS" option in the View preferences.

 

[Interference]

I saw some REW screenshots here that shows the DR (Dynamic Range) value on the RTA Window, which setting do I need to enable to show the DR value?

I also couldn't set the REW generator to 0 dBFS, only -3 dBFS, any setting to enable the 0 dBFS on the function generator? Thanks!

You should use the latest REW beta, where you should be also able to display THD and N in dB instead of %.

Note that REW will now show you either the A-weighted THD+N in whatever unit you choose for the y scale, or the THD+N relative to the test signal.

You have to calculate the DR by yourself:
DR = (max output level [dBy]) - (THD+N @ -60 dBFS [dBy])
where 'y' is whatever reference you use, for relative differences it does not matter. Just do not confuse the dBFS of the device output with the dBFS of the device input. Or just test the max output level and measure the SINAD (opposite of dB value of THD+N).

 

[Earfonia]

Noted with thanks @JohnPM and @Interference ! Will try the newest Beta version later!

 

[Earfonia]

You should use the latest REW beta, where you should be also able to display THD and N in dB instead of %.

Note that REW will now show you either the A-weighted THD+N in whatever unit you choose for the y scale, or the THD+N relative to the test signal.

You have to calculate the DR by yourself:
DR = (max output level [dBy]) - (THD+N @ -60 dBFS [dBy])
where 'y' is whatever reference you use, for relative differences it does not matter. Just do not confuse the dBFS of the device output with the dBFS of the device input. Or just test the max output level and measure the SINAD (opposite of dB value of THD+N).

Recently I read that this -60 dBFS DR measurement method is from AES17.
It is probably accurate enough for DAC output DR, but for amplifier, isn't the noise floor going up and down with the volume? Especially amp with analog volume control. So that means measuring noise floor at -60 dBFS and then add 60 dB to calculate the DR at maximum volume is not accurately reflecting the actual DR at maximum volume, because at max volume noise floor will be higher than at -60 dBFS. Is my understanding about this measurement correct?
Thanks!

 

[Interference]

Recently I read that this -60 dBFS DR measurement method is from AES17.
It is probably accurate enough for DAC output DR, but for amplifier, isn't the noise floor going up and down with the volume? Especially amp with analog volume control. So that means measuring noise floor at -60 dBFS and then add 60 dB to calculate the DR at maximum volume is not accurately reflecting the actual DR at maximum volume, because at max volume noise floor will be higher than at -60 dBFS. Is my understanding about this measurement correct?
Thanks!

The volume in most amplifiers is usually an attenuator potentiometer on the input. The amplifier gain is fixed.


Look up one of the power amplifier reviews on this forum. What you see in figures of %THD+N vs power is that you have three regions:
- a region with mid level of THD+N gradually descending, dominated by noise;
- a region where the amp performance is optimal and the THD+N has a plateau on the minimum;
- max power: steep increase due to clipping.

In general I don't find the DR of a power amplifier to be a very useful metric, since it's related to its max power. As Amir does, THD+N measured around ~5W (normal operating conditions, but this depends on your listening level and speaker sensitivity) can be more representative of what matters in normal operating conditions.

Take my words with a grain of salt as I am self-taught on these topics

 

[Earfonia]

Well, that's true for potentiometer that placed right in the input of the amplifier, but sometime amplifier input might have active component like buffer before the potentiometer. For that case turning the potentiometer down to measure the -60 dBFS noise will 'hide' the noise floor from the active input stage.

Anyway, I agree it is not a very useful metric, and the 3 regions of %THD+N vs power on the graph is a lot more useful to show the amplifier performance. But the problem is very rare to see manufacturer showing that kind of measurement and graph. Most often is just DR / SNR at max output.

I think many of us here are self-taught, that's what this forum is for, so we can learn from each other.

 

[hyperknot]

@Interference is a second hand E-MU 0404 USB a good choice for measurements from a Macbook? I'm looking for entry-level / beginner measurement instruments and I found one locally for about $48. Does it work out of the box on recent macOS?