DACs Reconstruction Filters

[mikitm]

Hi, I've been following this forum for a while and I believe it's one of the best out there for audiophiles and reviews.
(25yo from Italy here, sorry for bad english)

I was wondering about DACs and something peculiar came to my mind this morning, but first a couple of questions to clarify some stuff that I'm not 100% sure about.
(only regarding playback through foobar2000 with asio plugin and the latest topping driver)

1) I have a Topping DX3 Pro (thanks to this forum btw) and it's capabilites are 32bit/384KHz - does that mean that the DAC chip works natively at 384KHz and scales down to other sample rates when it needs to? Or is there no native sample rate, and just adjusts to whatever it's playing?

2) If a DAC's max. sample rate is 384KHz, how will it play perfectly 44,1KHz tracks? Can it be fixed in foobar2000? I've heard that Reconstruction Filters work best with multiples, i.e. a 96KHz track with a 384KHz Dac (96*4=384) but may cause clicks, dither or something like that when playing 44,1 / 88,2 and such.

I can't seem to find an answer to these questions, hope you'll be able to help me understand. Thank you!

 

[dfuller]

I am not the most informed on this one, but:

1) I have a Topping DX3 Pro (thanks to this forum btw) and it's capabilites are 32bit/384KHz - does that mean that the DAC chip works natively at 384KHz and scales down to other sample rates when it needs to? Or is there no native sample rate, and just adjusts to whatever it's playing?

All modern DACs oversample considerably, so no, that does not mean it works that way. The AK4493EQ in your DX3 Pro is a 5-bit D-S modulated part, and D-S by nature operates way above whatever the nominal sample rate is.

2) If a DAC's max. sample rate is 384KHz, how will it play perfectly 44,1KHz tracks? Can it be fixed in foobar2000? I've heard that Reconstruction Filters work best with multiples, i.e. a 96KHz track with a 384KHz Dac (96*4=384) but may cause clicks, dither or something like that when playing 44,1 / 88,2 and such.

That is not true and is a massive misunderstanding of how this stuff works.

 

[threni]

2) If a DAC's max. sample rate is 384KHz, how will it play perfectly 44,1KHz tracks? Can it be fixed in foobar2000? I've heard that Reconstruction Filters work best with multiples, i.e. a 96KHz track with a 384KHz Dac (96*4=384) but may cause clicks, dither or something like that when playing 44,1 / 88,2 and such.

Where did you read that?

My oven goes from 0 (well, room temperature!) to 250 degrees C. Doesn't that mean it'll burn my food if I only want to heat it to 100 degrees? No. It'll just heat it to 100 degrees.

 

[DVDdoug]

DACs Reconstruction Filters

Cheap soundcards...

One day at work I connected my oscilloscope to my soundcard's output. (I don't remember the purpose of the experiment.) I was shocked to see totally unfiltered stair-stepped waveforms! I just had some "little computer speakers" for listening to MP3s at work "after hours" and I never heard any distortion or anything "wrong". When I thought about it, the harmonics are above the audio range and speakers would filter them out.[/quote][/quote]

 

[AnalogSteph]

Cheap soundcards...

One day at work I connected my oscilloscope to my soundcard's output. (I don't remember the purpose of the experiment.) I was shocked to see totally unfiltered stair-stepped waveforms! I just had some "little computer speakers" for listening to MP3s at work "after hours" and I never heard any distortion or anything "wrong". When I thought about it, the harmonics are above the audio range and speakers would filter them out.

There must have been a bug of some sort involved - soundcards and onboard audio chips are basically all delta-sigma so definitely need a reconstruction filter. Remember what it was?

 

[mikitm]

Glad to hear that was bs from local audio "guru" guys I met online. Thank you for your answers!

 

[MRC01]

... 1) I have a Topping DX3 Pro (thanks to this forum btw) and it's capabilites are 32bit/384KHz - does that mean that the DAC chip works natively at 384KHz and scales down to other sample rates when it needs to? Or is there no native sample rate, and just adjusts to whatever it's playing?
...

... That is not true and is a massive misunderstanding of how this stuff works.

Actually it's not far from true, perhaps a small misunderstanding but not a massive one.

I'm not sure what your DAC does, but one DAC chip I'm familiar with, the WM8741, works similar to how you describe. It has a max input rate of 192, a max internal rate of 384k and oversamples the input at the highest integer multiple that is equal or less than that maximum internal rate. Then of course it applies an AA or reconstruction filter; it has 5 different built-in filters that are selectable by the implementation.

For example: if the input is 192k, it 2x oversamples to 384k. If the input is 48k, it 8x oversamples to 384k. If the input is 44.1k, it 8x oversamples to 352.8. etc. It always oversamples at an integer multiple because that simplifies the calculations required.