On a good day, an audio system can evoke Qualia - a subjective consciousness experience - rather than just present great hi-fi. You know the experience: the instruments sound real; the musicians and singers are present in front of you and you feel like you are at the venue. All audio components in the chain play a part in creating this magic but, with regard to a DAC, RF noise is causal. As I've previously indicated, it's only with near zero levels of RF noise that the DACs small signal processing or clock crystal oscillator circuit is sufficiently unperturbed so that our brain suspends disbelief and we accept the music we hear as being the real thing.
My reference system regularly induced this Qualia during my listening sessions and I believed I was near endgame. During recent tests, however, I replaced my Analysis-Plus interconnects with much higher priced Cardas Clear-Beyond and Allnic Zero-Loss and heard much more information and experienced more frequent sessions of Qualia bliss. I knew that all interconnects (regardless of price) faithfully conduct an audio signal ...so it meant that RF noise was entering the DAC via its outputs. I'll repeat: the interconnects were a two-way street with in-band audio signal going out and out-of-band RF noise coming in. I was amazed ...and also frustrated that my reference system still needed work. It seemed that the extra spiral construction of the Cardas and the braided Mu-Metal shield on the Allnic were somehow attenuating RF/EM noise through electromagnetic interference/cancellation. Also, it was clear that my DAC was being affected by RF noise radiated by sources well distant from my audio rack.
So, I put my house under RF lockdown to test resolutions to this issue that did not require spending thousands on cables. The drawing on the left shows my home with my dedicated listening room on the main level and all the usual household suspects for RF noise:
- switch mode power supplies
- household electronics
- computers, networking, wifi repeaters
- LED & CFL lighting
The drawing on the right shows my home gone dark except for listening room essentials. Devices and lights were turned off and power was supplied with batteries or on-line (double conversion) UPS power to avoid connection to AC wiring as an extended antenna. Of course, RF sources like WiFi or AC generators from neighboring homes were still present and able to affect my system.
To my pleasant surprise (expected but still nice to see validated), my reference system was noticeably more enjoyable with less environmental RF present ...and the expensive interconnects revealed much less positive benefit. The out-of-band RF noise level measured by my Signal Hound BB60C at Hugo2's output indicated a significant reduction in RF spectrum energy. Alas - this was likely subject to RF noise ingress through my thin coax test cables and variability in time-of-day and changes in electronics usage ...so I'll take the reduction in energy as valid but not the amount of change. The BB60C does not measure magnetic field strength so I used a TriField TF2 EMF Meter to measure a small (0.3mG to 0.2mG) reduction in magnetic field strength near the AC wiring.
I obviously could not impose a permanent lockdown on my family so I restored all electronics and worked on ways to improve my reference setup for better RF isolation. I was unsure of which frequency range I needed to address or how much attenuation was required so I applied successive layers of RF (and Magnetic) shielding until I began to more reliably experience Qualia during listening sessions. On the DAC outputs, I designed and tested filters that blocked RF noise coming in while allowing the in-band signal output to be as transparent as possible. I am now working on productizing my solutions. We don't know enough about our ear/brain to explain why we can hear the DACs response to these insanely small levels of RF noise but I know that my solutions are going to be a step toward a revolution in our understanding.