How to Do a Robust Digital to Analog Audio Comparison Using Roon

What does your digital to analog convertor sound like? One way to start to get a handle on a DAC's sonic character is to compare it to another one. The problem is how do you set up a robust, easily repeatable test? One way to simplify and enhance the A/B process is to use Roon-compatible DACS and use Roon as your playback application.

AR-Roon225.jpgWhy Roon? What makes it better for A/B comparisons than other comparable playback Apps such as Audirvana, Amarra, or Pure Music? Several factors make it superior.

The first feature that makes using Roon as a source so great for A/B tests is a feature called "grouping" which allows you to send the same signal to more than one device simultaneously. And you can choose which devices to group together. So, two DACs can receive exactly the same signal at exactly the same time. This allows you to switch from A to B almost without a pause. The only limiting factor is how quickly can you go from DAC A to DAC B via your preamplifier controls or signal switcher's remote. 

AR-ProjectDAC225.jpgThe second thing that makes Roon ideal for DAC A/Bs is that it is using the exact same RAAT protocols for both DACs. According to Roon, "RAAT is plumbing. It gets the audio from point A to point B without screwing it up, and without bringing limitations to the table that might compel the software/hardware on either side of it to screw things up. It's an enabling technology for "doing things right" everywhere else in the system." So, in theory, the RAAT protocol shouldn't favor one DAC over another one.

Also, unlike most A/B comparisons when you are comparing two different players or music apps where you must try to synch the same track or music file on two different apps or players so that each DAC being compared is playing approximately the same music at the same time (which is sort of essential for a robust A/B comparison), using Roon two tracks are always in perfect synch because there's only one track being played simultaneously through both pipes.

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There are still situations that can slow down even this seemingly instantaneous A/B test - if the two DACs being compared are not outputting the same volume levels. Unfortunately, this is a common problem. I recently compared the Project S2 Pre with the Benchmark DAC3B through the new Benchmark HPA4 analog line-level preamplifier and headphone amplifier using Roon as my source and ganging Roon's output to these two DACS. After only 30 seconds of listening it was obvious that the Benchmark had a slightly higher output level than the Project and I could identify it in a blind test ten out of ten times. The solution was to turn down the volume level on the Benchmark to match the Project, since I could not turn the Project up past 0 db. But to do this I would need to know which DAC was which, hence it would no longer be a blind test. To re-blind it would require an additional human to adjust the volume when switching sources.

AR-DAC225.jpgOut of curiosity I played a sine wave file and measured each's DAC output level. The Benchmark was consistently .2 dB louder according to several SPL Apps on my iPhone. .2 dB is not very much. Unfortunately, the HPA4 has .5 dB increments to its volume adjustment, so I will need to find another preamplifier that allows for finer adjustable increments to do a proper level-matched test. 

But during preliminary undisciplined listening, except for that slight volume difference the two DACs, they sounded scarily similar despite their different prices and internal technologies, which is why I do A/B tests...Roon certainly makes that comparison job quicker to set up, simpler to use, and produces more robust end results. 

So, if you're itching to do some serious and robust sonic comparisons Roon could make your life much easier; and it's also not too shabby for just listening to music...

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