Music in the Round

Sidebar: Did I Really Prefer SPL's Pro Devices to My Audiophile Preamps?

As a test, I did something I'd long considered trying but had always put off: I connected my exaSound e38 DAC directly to my power amps. This limits my choice of source components to my server, and to controlling the volume with only the up/down buttons on the exaSound's front panel, or an elusive little Apple remote control. What I discovered was that the effect of inserting each SPL box was almost inaudible. Maybe I perceived a little bit of softening of the highs, but no change in overall balance or resolution. Briefly—though only after a lot of cable-thrashing—I tried the same comparison with the Audio Research MP1 and the Parasound Halo P 7 and, dammit, they didn't sound much different either—but both, particularly the ARC, added some high-frequency noise.

That immediately reminded me of the phenomenon of stochastic resonance, which is often cited to explain why one can hear low-level signals that are below the noise threshold. Briefly, the principle is that subthreshold but salient signals, like music, become audible as concurrent frequencies in the random noise add to them. The ear can then distinguish the sum of the signal plus noise as a distinct pattern recognizable as the music signal.

I am positing that the ARC's audible HF noise works the same way to statistically emphasize higher audio frequencies that are below or above threshold. I can hear the hiss from my listening position when I turn the MP1 on, but my ears quickly adapt to it, and since it usually remains on, I'm usually unaware of it. That doesn't mean it isn't contributing a stochastic influence on the audible treble. I take it as consistent with my supposition that the much quieter but still not silent Parasound produced less treble emphasis than the ARC. Running the power amps from the exaSound e38 DAC or via SPL's Volume 8 or SMC 7.1 produced no noise from the speakers unless my ear was actually in contact with a tweeter.

Unfortunately for my hypothesis—from which I am not retreating—the published noise specs for the SPL boxes are not better than that for the Parasound, but they sound quieter than the Parasound or the Audio Research—although the exaSound e38 measures and sounds quietest of all. I just wish it had a volume knob.—Kalman Rubinson