I have noticed anecdotally that playback of 16/44 recordings through the DAC DSP card in high dynamic range portions of music sound like they are experiencing digital clipping, whereas higher resolution recordings don’t seem to clip. I suppose it could be the recordings, but it seems too consistent to be that, so I’m wondering if there a possible firmware update or level controls to the card that may be needed. There are many elements to the signal chain so ideally it would be good to figure out a way to test it. I run my music library through roon, which connects to an rp4 with a DAC-DSP HAT. Any ideas welcome. Thank you.
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HiFiBerry team We don't see this here. I also don't see why the sample rate should have an effect on this as a.ll internal DSP processing is handled at the same sample rate. You can try reducing the volume on the DAC to see if this changes something.
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Paul Rosen Hi there, thanks for the quick reply. I was thinking more the bit depth resolution, not the sampling rate. It seems that 24 bit recordings don’t have this effect where as many 16 bit recordings do. When I first got a hifiberry HD2 device, there was distortion that I reported to you and you recommended a register update, which fixed the problem. That’s why I thought maybe I need some other update or settings from you. I tried setting the headroom lower and enabled the clipping indicator and all seems normal, and turning the volume down doesn’t seem to make a difference, so perhaps it is just the recordings.
The music that seems most affected is voice, especially soprano. I thought maybe this was because the voice has a huge dynamic range and any clipping or distortion would be more obvious there. It is difficult to diagnose from recordings because I don’t have the same music at different sampling conditions, though I suppose I could create some. Do you have reference audio files to test different resolutions that you can recommend?
But I suppose it is possible that 16 bit recordings are just not well done. My brother tells me this all the time about his CD collection - lots of really poorly done mastering.
By the way, I have had very bad luck with the HD2 card. I have bought three and each as failed (or so it seems). I have used them to feed a homemade preamp, which normally I would blame for somehow breaking them, but all the other hifiberry dac devices I have work reliably with that preamp. Are there fundamental electrical differences between the HD2 and other devices that would make them more sensitive? Is there a way to diagnose if they are really dead or need to be reset in some way? Should I open a different thread to address this?
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HiFiBerry team Also the bits/sample are the same internally. The DSP processing internally is always handled exactly the same as the connection to the Pi is handled by a piece of hardware (ASRC) that converts the incoming audio stream to the sample rate and bit format of the DSP.
My guess is that the recording is simply not good. We don't have reference audio files. To detect clipping, "real audio" isn't really a good choice. You would use a simple sine wave and audio analyzer or oscilloscope for this.
In general, the DAC2HD is way more complex than the DAC2Pro. This means you can damage more things. My best guess (and it's just that) is some offset voltage on the input of your pre-amp that damaged the output stage of the DAC2HD. -
Paul Rosen OK, thank you. I guess you are implying that the ASRC doesn’t have any configurability and could not be doing anything to degrade the quality during conversion. I’ll think about whether it is worth doing sine wave tests or just explore more cd’s and their variability.
On the DAC2HD, is there a way to know what a damaging offset voltage would be for any of the hifiberry devices? I would like to get it to work, as the sound quality is really stellar, but I can’t afford to keep burning through them! Thanks for your help!
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HiFiBerry team The ASRC on the DSP works very well. I would not expect a problem with this.
Any offset voltage on the input of your amplifier can create problems as the DAC is DC coupled and therefore can't block any incoming voltage. Usually there should be a resistor and a coupling capacitor on the input of your amplifier to make sure, voltage without anything connected is zero. -
Paul Rosen Hmm. I don’t see a capacitor at the input, only a resistor but it feeds a tube directly, so perhaps it provides the needed capacitance. I’ll check with the designer, but I’m sure he will tell me it is designed for 0 DC on input. Is the HD2 design different from the other DACs in this regard. As I mentioned, the others all seem to work fine with this preamp.
Thanks so much for the help.
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Paul Rosen I measured the voltage at the input. It is 0 V. The grid to plate in the input tube configuration does act as a capacitor. I talked with the designer, and he said that unless there is a leaky grid, it should be 0 V, and it seems to be 0V.
I’m wondering: is there any HD2 board diagnostic that could be performed, either through measurement or self-test, that would provide an indication of what is amiss?
Thanks.
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HiFiBerry team No, there is no diagnostics you can perform. While you can send the DACs to us, we probably won' be able to tell you HOW they got damaged.
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