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In a 1990 Stereophile measurement, a CD player outputs 0dB square signal without clipping, which indicates digital headroom in oversampling filter. Compare Fig. 8 and Fig. 9 in the linked web page.
Do you know any off-the-shelf DAC chips with digital headroom?
I guess Sabre chips do not have digital headroom, since Benchmark is advertising digital attenuation before DAC chip for its DAC2.
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The SABRE chips have a 32 bit digital volume control. This can be used to provide as much digital headroom as desired. In the case of the Mytek Stereo192-DSD DAC which I have there are two ways of doing this. One is called "volume trim" and this setting remains in effect whether the user outputs the maximum analog output (bypassing the analog volume control), or if the digital volume control is selected (also bypassing the analog volume control).
Because the Mytek sounds better if other filters are used than those supplied by the SABRE chip, I use my PC and HQPlayer to upsample. I also use HQPlayer to do digital room correction. As a result, with loud recordings there can be occasional clipping in the computer. To avoid this, HQPlayer has its own digital volume control, which I've set for -3dB of attenuation.
Many DACs have non-linearities when driven with high level digital signals. It's not just digital clipping in the DSP. One needs to adjust the "gain staging" of ones system to get the best results. If one is still using a 16 bit DAC this won't be possible without throwing away resolution, but with a 24 bit DAC the recordings don't have 24 bits of resolution in the first place, so not much is lost by adding a few dB of headroom. With a 32 bit DAC nothing is lost, as the bits are just shifted down into the 8 extra zeros... The analog output circuits in the DAC and analog input circuits in the preamp may overload according to inter sample peaks and even if they do not they may sound better if not overdriven. In addition, it is possible to overdrive the input circuitry of some preamps. These tradeoffs can be evaluated by listening to music, but it takes some effort to find appropriate test recordings and what to listen for. My Mytek sounds much cleaner if it is not overdriven. I use the extra internal jumpers to lower than analog gain, and then use digital volume control in the Mytek (i.e. the SABRE chip) to control the output level. I do not care for the "warm" sound of the Mytek analog volume control which sounds to me like distortion.
Digital headroom is not unique. It is just correct engineering. It may not be common, but that's because vendors have gone for impressive noise specifications rather than good sound. This is just one example where there can be real engineering tradeoffs between "measures good" and "sounds good".
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
. . . and I've got my digital attenuation set for -2db. Is there a particular reason you went with -3db? Frankly, I haven't played around with the settings for HQPlayer very much yet, since I'm still mostly using Audirvana. The two players can sound surprisingly different, although I'm hard pressed to say right now which sounds better.
I set mine to -2 originally, as suggested. However, because I do some DSP to manipulate the bass there were still a few cases where I saw an overflow, as indicated by the "Limited:" counter incrementing. So I went to -3 dB.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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