[Funkstar De Luxe]

I just bought myself a MOTU 24IO for the studio, upgrading from an EMU 1820m.  I was wondering if there is software out there (preferably free software) that would allow me to make critical measurements from each of the interfaces.  Something that will let me loop input to output and analyse the return.  This would allow me to compare the real quality without my placebo ridden opinion getting in the way.
 
So, can anyone offer a suggestion or advice?
 
Thanks

 

[mikeaj]

The most common software for doing output/input loopback testing is RMAA, which has a free version (and is notoriously buggy, gets some calculations wrong, but it mostly works).  For fair comparison, maybe you should normalize the output levels to be consistent with a multimeter before running the program.  But what are you trying to measure?  It's not like running a loopback will let you isolate the DAC performance from the ADC performance—what imperfections you get will come from both.  There are also grounding and other instrumentation issues to consider as well.  To get fairly accurate measurements, you need real testing gear, which is expensive.
 
Check stv's posts in this thread as well, for some ideas of the challenges, fixes:
http://www.head-fi.org/t/609480/ok-so-what-can-i-reliably-measure-from-a-pc-soundcard
 
 
Of course, you could also write your own program to use instead of RMAA, or just record some test tones and do your own FFTs and analysis.  But for a quick check, RMAA is probably okay as long as you can get it to not spit out complete garbage.
http://audio.rightmark.org/download.shtml

 

[Funkstar De Luxe]

RMAA won't let me use ASIO output, which is really critical for me to test.  And yeah, loopback isn't just the DAC, but I feel it gives me a good real world benchmark.  Thanks for the links, I'm looking into them.

 

[stv014]

You can generate a WAV file with RMAA, create a loopback recording of that with any software that supports ASIO, and then analyze the results with RMAA.

 

[Funkstar De Luxe]

Excellent suggestion.  I did just that and seen a massive jump in quality from MME to ASIO.  Here's the RMAA results for a MOTU 24i/o if anyone is interested.  As can be seen there is some noise at 50Hz (I'm in the UK), and at the even and odd harmonics of that.  Quite a good result though I think.
 
Ignore the MME prefix of the files, I simply used that to generate the audio file and run it through my DAW using ASIO drivers.
 
results are here: %20PCI-424%20Analog%2023-24%20(MOTU PCI.htm]www.bassdress.com/tests/[MME]%20PCI-424%20Analog%2023-24%20(MOTU PCI.htm

 

[audiosampling]

Another way is to subjectively asses the quality of your DAC, with an objective test. The test uses a frequency sweep, which covers the whole frequency range of your DAC. Frequency range depends on your sample rate. For example, if the sample rate is 96 kHz, the frequency range extends up to 48 kHz (half the sample rate).

 

You can download such test files here: High Definition Test Tones Download

The sweep starts by playing frequencies that are in your hearing range, and then they will steadily increase. As the sweep enters ultrasonic range, the sound will fade away. Listen carefully; the rest of the file should remain perfectly silent!

If you hear anything while the file sweeps the ultra-sonic range, your DAC suffers from _severe_ aliasing. And it happens more often that one thinks! I am now wondering if aliasing could be the reason why some people prefer the higher sample rates...

I like this test, because it is very simple to perform and althoug loop-back testing such as RMAA is a fantastic tool, it will end up with figures that are sometimes difficult to interpret. With my suggested test, your ears will be the judge. If you hear something when you are not supposed to, you know that something is wrong that that something is audible! If you don't hear anything wrong, there might be some deficiencies left, but at least you know that you don't hear them.