I'm building audio (wave) player on some microcontroller.

I will have external 16-bit DAC and I wonder if that's enough? I mean, is low-pass filter really needed? (I know what it does and why you use it after DAC, but will it be hearable if there is no LPF?)

So my question is: do I need anything more then just DAC? If I set DAC value and put its output (without any additional buffer/oamp) to speakers (from my PC, with built-in amp), will it work? (I'm planning to use DAC8531E as DAC).

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    \$\begingroup\$ The first place I would look is at the typical application circuits in the DAC's datasheet. (not the testing circuits) I haven't looked it up yet, but that's usually a good starting point. \$\endgroup\$ – AaronD Oct 20 '15 at 14:19
  • \$\begingroup\$ Although you might not hear them there can be high frequency components that an amplifier will amplify and a speaker will try to reproduce. In my opinion there must ALWAYS be a LPF after a DAC. Note that although in the DAC8531 there's no LPF filter, there actually is ! It's the opamp. But I would still include a simple RC filter with a cutoff of 100 kHz or so, just to be safe. \$\endgroup\$ – Bimpelrekkie Oct 20 '15 at 14:24

If you want decent quality then you'll need a reconstruction filter and a low pass filter. Clearly the low pass filter is to prevent unwanted HF quantization noise being forwarded to whatever is connected to the output but, the DAC reconstruction filter does something that all decent quality DAC systems need to consider. It corrects for the fundamental amplitude error produced in all DACs. Consider this: -

enter image description here

The digital input signal to the DAC is totally flat in the pass-band and then after the DAC and low pass filter (flat to Fs/2) there is a loss of signal level at the top end of the spectrum. This is natural for all zero-order-hold DACs (this includes the DAC8531).

That attenuation starts happening as the desired frequency starts getting a little close to the sampling frequency. This is the formula that describes the attenuation: -

enter image description here

Where f is the desired frequency and fs is the sampling frequency. A couple of solutions might be: -

enter image description here

Here's a very good article from Maxim where I stole the pictures. If you aren't too bothered about a 3 dB loss at the high end of your spectrum then I wouldn't worry about all of this. The DAC8531 is barely hi-fi quality so it probably doesn't matter.

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  • \$\begingroup\$ Ok, so if it's not very hearable I won't probably use those filters. Or maybe you know some audio DAC IC that already include such filters? \$\endgroup\$ – zupazt3 Oct 21 '15 at 12:59
  • \$\begingroup\$ I don't know of any because the filter would depend entirely on the sample rate used and the design aim of highest pass frequency and these are such big variables. Maybe there might be an audio DAC with the filter in because sampling rate is normally 44.1 kHz and ftop is normally 20kHz. \$\endgroup\$ – Andy aka Oct 21 '15 at 13:23
  • \$\begingroup\$ Well, I've just found one - made specially for audio and includes filters, resolution even up to 24 bits: UDA1334ATS nxp.com/documents/data_sheet/UDA1334ATS.pdf \$\endgroup\$ – zupazt3 Oct 21 '15 at 14:04
  • \$\begingroup\$ Yeah that looks really cool and it's stereo and really very cheap. Good find. \$\endgroup\$ – Andy aka Oct 21 '15 at 14:13

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