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I am not an audiophile. I have heard many times that hardware X has good/bad DAC. The "has" signifies that DAC is a kind of separate chip inside it.

As far as I know, DAC is an algorithm to fill in the blank from digital number samples to voltage output. Isn't this achievable by any computers today? Can we change the quality of DAC just by rewriting the algorithm?

For example, "iPod Touch's DAC is not bad". Is it possible for Apple to issue an update that will improve the algorithm to make better analog signal from digital numbers?

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The ADC (Analog-to-digital converter) and the DAC (Digital-to-analog converter are the gateways between the real analog world of electrons and the digital binary world; While it is possible that some converters are controllable via firmware/software and thus conceptually are upgradeable, it fundamentally imperative that some sort of hardware exist that realize the electrical conversion, either by sampling and quantization (ADC) or reconstruction.

Here is the whole process illustrated: enter image description here So the DAC quality is all about how well the reconstruction from curve 3 to curve 4 is carried out. Both hardware and the controlling software/firmware has influence here, but in the end the hardware sets the limit to what can be achieved, and what is controllable with software and what is not varies greatly with different DAC hardware. Thus it is not possible to give a general answer to your question - it depends on the hardware.

If you want a technical introduction to the ADC/DAC topics, take a look at this slide

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Your title question is different to the main question you ask in the body of your post, so you may want to change it a little! However, in response to your main question:-

DACs, whether external audio interfaces, or the internal audio chip in your cellphone, are just like any other piece of hardware; their performance can be tweaked and (possibly) improved by updating software / firmware, but ultimately they are restricted by the quality of their physical components and electronic design.

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Look at the bigger picture, if any computer be it an ipad, or the music player on your iPhone were capable of producing high quality digital conversion with simple software updates then companies like Apogee wouldn't be so renowned. Their converters cost thousands. And with good reason. High quality DAC will have superior reconstruction filters etc.

  • That's what I am thinking too. But maybe I am comparing this to GPU. Graphic cards are separate hardware because normal CPU is not specialized in number operations that draws image on the computer screen. There are many such commands to be compute per frame that it worth having separate specialized hardware to do it. But for DAC, I did not think that it is that computationally expensive, but requires many researches for good algorithm. (Audio is just a sequence of numbers anyway?) That's why I thought they can be the same one as the CPU. – 5argon Sep 14 '16 at 4:35
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    No matter where the 'processing' of the digital-to-audio conversion is performed, you still need the hardware to interface it with the 'analogue world'. As in my above answer, the ability to 'accurately' perform the digital-to-analogue conversion will be restricted by the physical components and the design of their circuitry. Whilst digital "audio is just a sequence of numbers", it is still quantised; higher quality DACs will be better at reconstructing the original analogue signal more accurately than cheaper ones, that have a more basic design and cheaper components. – Skarik Sep 14 '16 at 5:30
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DACs use oversampling in order to split the antialiasing filtering between hardware (where high-order low-passes lead to bad signal-to-noise ratios and high dependency on circuit tolerances) and software (which requires considerable computing power but has low noise and high quality).

If you can afford the computational costs of higher oversampling, the results will likely be better by having lower requirements from the analog circuitry. You cannot, however, entirely replace the analog filtering. Sampling will always lead to aliasing which requires analog circuitry to deal with.

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    Your final sentence is a bit misleading - it is absolutely possible to remove aliasing with digital circuitry, and the most common technique is just to ensure it is up in a frequency range that won't cause any audible artifacts – Rory Alsop Feb 13 '17 at 16:51

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