Question: I'm currently attending a basic course on real-time embedded systems. Recently, we have been talking about embedded systems memory architecture. When doing some extra studying on memory maps, I came across the memory map for the ATmega328P microcontroller. As can be seen from the image, the flash is divided into a boot section and an application section.

[![enter image description here](https://i.stack.imgur.com/NWBNO.png)](https://i.stack.imgur.com/NWBNO.png)

Why is the boot section not starting from address 0? As I've understood it, the microcontroller application won't run without a bootloader. So why doesn't the bootloader occupy the lower addresses if everything else relies on it?

Answer: 
Well, even your first assumption is wrong.

Audio DACs are these days are not even constructed from R-2R resistances. Even a 1-bit delta sigma modulator will likely have better specs on audio bandwidth than a bunch of resistors. The problems of analog domain are handled by processing in digital domain.

Usualy the price of a product is just dependent on how much money and effort has been made designing it, so careful design generally makes a more expensive product. Careful design includes selecting and evaluating reliable quality components, designing the schematic and good PCB layout, maybe even using a more expensive 4 layer PCB, and maybe the look, feel and materials of the case to justify the high price. It may include more software features than other products, so it takes longer and more money to develop features that may even be rarely used.

But remember that selling a good looking product at a high prive does not mean it's Hi-Fi, it's the specs.

And sometimes, these devices go just overboard with the specs, maybe forced by the marketing department. For example, your ears hear up to 20 kHz, and likely the material you play is recorded to 20 kHz, so why would you need a DAC, amplifier and speakers that can play up to 40 kHz unless you are a bat.
I can't add much to the above excellent contributions, except to add that if you have a voltage available of 30V pk-pk in the analogue domain, then 16 bit resolution equates to about 460uV pk-pk or around 160uV rms. So if your analogue circuitry is not giving less than this as noise - across the full 10 octaves of the minimal audio range (20Hz-20kHz) that is - further discussuions about the resolution of the converter are probably looking at the wrong thing.

For reference that -160uVrms is -74dBu. In my experience of making audio measurements, if you measure less than -80dBu output noise in a typical circuit, you're doing OK. -90 is very good.

And that is with +/-15V rails on the analogue side of the converter - if you are dealing with only 6V or 3V3, and 24 bits, sampling at 96kHz, of course it all gets even more difficult.

If you are making an ADC, you are likely samping a lot of low level analogue noise from input circuits.

If you are making a DAC, the output noise of your gain stages following the DAC might be more important than the DAC itself.

In reality I suspect many "high end" ADCs/DACs with 24bit resolution are actually losing at least a few bits just because of analogue domain stuff.

If you are curious about whether or not you can really hear all those bits, [the redoubtable Ethan Winer has some interesting things to say about it here](http://ethanwiner.com/BitsTest.html). You can even take part in his interactive test by downloading and listening to some files.