I was reading a review of the Benchmark Audio DAC3 today on Dagogo.com and in the review, Doug Schroeder talked about the utilization of the headroom option in Roon and how enabling the function on the DSP settings and changing the value markedly changed the sound. Apparently this is because of design of most DACs that are overloaded during upsampling. This is the explanation provided by Benchmark’s John Siau:
“It is a gain reduction function that reduces the signal level before any DSP operations occur. This also reduces the signal level going to the DAC. This reduction provides enough headroom to prevent DSP overloads. Most importantly, it prevents the gross DSP overloads that can occur when an upsampling function reconstructs the audio waveform between samples. All sigma-delta D/A converters use oversampling or upsampling. The headroom function prevents the digital clipping of intersample overs (signal peaks that exceed 0 dBFS). Benchmark converters have an extra 3.01 dB of headroom in the entire digital path and the Roon headroom function should be turned off (or be set to o dB). Virtually all other D/A converters will benefit from this function. In my opinion, this should never be set less than about 1.5 dB and it should be set at the full 3 dB if MP3 files will be played. I have written six papers on the topic of intersample overs. The people at Roon and JRiver are aware of the intersample over problem, but sadly, most converter manufacturers have ignored this issue. Intersample overloads generate false high frequency percussion sounds. This defect is entirely preventable using the headroom function or a DAC with built-in headroom.”
So it got me to wondering if the Directstream was immune to this problem. So I went into the DSP of Roon and picked a particularly hot section of Santana’s Black Magic Woman ripped from the Ultradisc Abraxas. I record in Vinyl Studio with the option on 0 dB headroom since I’ve never noticed distortion during playback. According to Roon, if there is distortion, the signal path light will go red. Hopefully you would also hear distortion while this is going on, obviously. No red light and no distortion to my ears. I then gave it -3 headroom and it was not only a bit quieter, but also slightly less dynamic, but this might be my imagination. I then dug out some of my harder hitting music recorded in MP3, files of which which I haven’t listened to in forever. I tried Soundgarden Superunknown MP3 multiple songs and got no distortion, visually or audibly. Likewise Nirvana’s Nevermind in MP3 was free of distortion. My guess is that the Directstream is immune to this problem John Siau speaks of. When he says “Virtually all other DACS will benefit from this function”, I guess the rare exception would be the Directstream. And, I guess the Benchmark DAC3.
Here’s the link of the section of the review that Mr. Schroeder talks about this:
I will note that he talks of being able to change the headroom from -3 to +3. My version of Roon only allows -3 to 0. I’m not sure if this is an error on his part or an idiosyncrasy of DSP settings with his DAC.
So what do you say, @tedsmith? Am I correct in thinking that the Directstream is immune to these problems? Thanks!