PAR Opinion: How to Choose a Digital Converter

With Pro Audio Review Tech Editor Lynn Fuston
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1993 was the year when I first started comparing ADCs. I was mixing from 2-inch to a Panasonic 3500 and I wanted a front end that sounded better. I compared the significance of the A/D stage and D/A stage on the sound and found that if I had a great AD stage, any and every subsequent DAC reflected that sonic improvement. Since most of my work was headed to professional mastering, where they utilized expensive DACs, I didn’t really need an expensive DAC for playback in the studio. I compared all the converters I could get my hands on (which wasn’t many at that time). I was impressed with and ended up buying the Mytek 2018 ADC because it sounded the best and the center image was very stable, unlike any other converter I heard.

What differences might one hear when auditioning ADCs? First off, the differences between converters will be subtler than between mics or preamps. Apart from the obvious issues of noise and distortion (even inexpensive converters these days offer real-world performance of 85 dB signal to noise—and 105 dB+ specs—plus distortion in the 0.001% range), what separates the sound of different converters? I listen for tonal balance, separation, low level detail, imaging and integration.

What To Consider

Tonal balance: While the broad definitions of warm or bright may not apply as with microphones, there are still perceptible tonal differences. Some converters will sound brighter or fuller than others. Even though all converters these days will probably spec within fractions of 1 dB from 20 Hz to 20 kHz there are still differences in the frequency balance.

Separation: I like to hear separation between the instruments, so I can pick out the details of individual instruments within the mix.

Low level detail: This is an area where major differences can be heard. Sounds like harmonics or reverb trails are supremely telling when it comes to comparing converters, with reverb sounding choppy or smooth as it trails away.

Imaging: On some converters, the sounds just seem to mush together into a big flat wall of sound, while others will offer depth and breadth to the sound, with a life-like quality.

Integration: This is the most esoteric of the categories. When I conducted the listening tests for my 3D ADCD in 2002 (a CD with side-by-side listening tests comparing 29 calibrated ADCs), the biggest difference between the best and worst converters was the ability to convey music without it sounding like it was being processed at all. The highest praise I can offer any ADC is that, when I am listening back, it just sounds like music and I forget about the technology. It sounds simple but it’s an elusive goal.

Evaluation Tips

So how does someone set up a comparison test for evaluating ADCs? Here are some tips.

•Pick the highest quality source that you have available. On the ADCD, I used three sources: a remix from 2-inch master tape (all analog), a big band recording from a DSD-sourced SACD and a mix sourced from RADAR. Non-digitized sources are always preferable.

•Calibrate. This is absolutely crucial, since differences as small as one-tenth of a decibel can effect your perception of any sound. Use a test tone and the meters on a console or workstation and calibrate the ADCs to within 0.1 dB.

•Make sure all the clocking is properly addressed. I prefer to run all the converters on their internal clocks since they were designed to work that way.

•Listen at the same level. Pick a comfortable listening level and listen to all the converters at that level, without ever adjusting the volume knob.

•Keep your head in the same place. Pick a listening position and stay there. Even in very good listening rooms there are standing waves and reflections and nulls that will impact your perception.

•Listen blindly. If at all possible, do NOT know the identities of the converters you are testing. Perception bias is a phenomenon where people choose what they like based on its perceived value or some other attribute. Only by not knowing the identity of the converters as you listen can you make an honest assessment.

•Trust your first impression. It’s easy to rationalize what you hear after the fact. I listen with a piece of paper and pencil in hand. I write down the first thing that comes to mind. In a recent shootout, I wrote down “hard” for one and “smoosh” for another.

Recently I joined Glenn Rosenstein (Ziggy Marley, U2, Madonna) and David Kalmusky (Journey, Small Town Pistols, Emerson Drive) at the new Addiction Sound in Berry Hill, TN to listen to converters. The contenders included Digi 192, Avid HD I/O, Crane Song HEDD 192, Antelope Orion 32 and my early 1990s SV-3800 for historical perspective. We listened from a half-inch 2-track master. The source was routed through the converters at 48 kHz and returned to the Trident TSM console, each identified only by letter. We listened one at a time on ADAM S4X-V, Yamaha NS10M or DynAudio Air 6 monitors. After listening, we compared notes. Our observations were surprisingly constistent, though our preferences were not. We all noted a “family resemblance” between the Avid converters with Glenn preferring the 192 and David choosing the HD interface. I preferred the HEDD. So each engineer preferred the sound of the converter that he uses. And we each stated our preference before the identities of the converters were revealed. Fascinating and somewhat surprising.

Ultimately, the choice of a converter is a very personal one, just like choosing mics or speakers. Although it’s not the most sonically significant item in the recording chain, if you’re recording to digital, everything you record will have that sonic imprint on it. So it’s a critical component. Listen carefully and pick the one that best preserves all your engineering craftsmanship.

To order 3D Audio Inc.’s ADCD:

Lynn Fuston is a Nashville-based recording engineer and mixer, owner of 3D Audio, Inc., and the Technical Editor for Pro Audio Review.