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What is the DAC of 4x10HD like? 8 years 2 months ago #14626

  • tcpip
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Can you please give me some details of the DACs at the outputs of 4x10HD? After the DSP does its work, when the digital audio is to be converted to analog, what is the sample size per sample which is fed to the DAC? Is it 24 bits? 16?

Also, how is the volume control implemented? Is it implemented by applying DSP and reducing the number of bits fed to the DAC, or by changing the Vref of the DAC in the analog area (if such a thing is possible)?

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What is the DAC of 4x10HD like? 8 years 1 month ago #14635

  • Jim the Oldbie
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Can you please give me some details of the DACs at the outputs of 4x10HD? After the DSP does its work, when the digital audio is to be converted to analog, what is the sample size per sample which is fed to the DAC? Is it 24 bits? 16?


The DACs are 24-bit, at either 48 or 96 KHz, depending on which plugin you're using.

Also, how is the volume control implemented? Is it implemented by applying DSP and reducing the number of bits fed to the DAC, or by changing the Vref of the DAC in the analog area (if such a thing is possible)?


I'm pretty sure it's that first one; the signal is multiplied (divided?) by the attenuation factor (volume setting) before going to the DAC. Hopefully someone will correct me if this is wrong. I'll admit that I'm not crazy about this idea on paper; however I've been using mine like this at length and haven't heard a single thing to complain about. Looks to me like as long as the analog gain structure is correct, digital volume seems to work rather nicely.

Incidentally, for what it's worth I've always found my 4x10HD to have a nice, smooth sound, especially in the high-frequency area. I haven't used the analog inputs much, but I can report that the DACs in this unit sound pretty good to me, and I suppose the sample rate converter on the digital ins must be doing a proper job as well.

-- Jim
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What is the DAC of 4x10HD like? 8 years 1 month ago #14636

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Any inputs from anyone? Please?

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What is the DAC of 4x10HD like? 8 years 1 month ago #14637

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The DACs are 24-bit, at either 48 or 96 KHz, depending on which plugin you're using.

Thanks a lot. I can see in the documentation that the DAC IC is 24 bit, but this is not a guarantee that the DSP circuit is feeding 24-bit samples to the DAC. Therefore I was keen to know. I presume that the DSP is feeding full 24-bit samples to the DAC?

I'm pretty sure it's that first one; the signal is multiplied (divided?) by the attenuation factor (volume setting) before going to the DAC. Hopefully someone will correct me if this is wrong. I'll admit that I'm not crazy about this idea on paper; however I've been using mine like this at length and haven't heard a single thing to complain about. Looks to me like as long as the analog gain structure is correct, digital volume seems to work rather nicely.

Actually, if the DAC is receiving 24-bit samples, then attenuation in the digital domain will work well enough. We rarely need attenuation of more than 60-70 dB, and if sample size is 24-bit, then there are more than 16 bits left over even after attenuation, at low volume settings, to give us very clean analog outputs. That was the reason I was trying to find out about the sample size.

Incidentally, for what it's worth I've always found my 4x10HD to have a nice, smooth sound, especially in the high-frequency area. I haven't used the analog inputs much, but I can report that the DACs in this unit sound pretty good to me, and I suppose the sample rate converter on the digital ins must be doing a proper job as well.

Thanks a lot. Am keen to finish my project and see how the whole rig sounds. :)

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What is the DAC of 4x10HD like? 8 years 1 month ago #14638

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DAC is connected to the DSP via I2S. These I2S data lines are also available at the expansion header e.g. for connection of miniAMP or miniDIGI. Both AMP and DIGI state in their user manuals that they use 24bit I2S and therefore I am quite sure also the connection between DSP and DAC is 24 bit ;)
As Jim already mentioned volume control is handled in the digital domain by the DSP (min. 24bit but probably 28bit, which is the internal bit depth of the DSP) and works really good in real life if analog gain structure is done right.
kind regards, Daniel

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What is the DAC of 4x10HD like? 8 years 1 month ago #14639

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DAC is connected to the DSP via I2S. These I2S data lines are also available at the expansion header e.g. for connection of miniAMP or miniDIGI. Both AMP and DIGI state in their user manuals that they use 24bit I2S and therefore I am quite sure also the connection between DSP and DAC is 24 bit ;)
As Jim already mentioned volume control is handled in the digital domain by the DSP (min. 24bit but probably 28bit, which is the internal bit depth of the DSP) and works really good in real life if analog gain structure is done right.

Thanks a lot. All my questions are answered. And I am sure that (given a good DAC), volume control in the digital domain will work perfectly well with 24 (or more) bits sample size. All the worries about losing bits and hearing quantisation noise only apply if we start with smaller sample sizes where the attenuated amplitudes are less than about 15-16 bits FSD. Don't you think so?

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