Would upsampling in Audacity just change the distortion, without improving anything that could be heard on a DAP then?
Upsampling from 16 to 24 bits does nothing, except make a bigger file with an extra byte (8-bits) full of zeros.* It’s mathematically lossless and completely reversible.
Increasing the sample rate is “mathematically imperfect” but it’s audibly perfect. Of course, you shouldn’t do it unless you have a good reason. For example, if you are converting from CD to DVD, you’ll have to upsample to 48kHz.
Intuitively, it seems “better” to convert between 44.1 and 88.2kHz than between 44.1 and 96kHz, but in practice there is filtering which involves rounding, the DSP is the same, and there’s no advantage to “even numbers”.
And here’s where I need a reality check. If I’m understanding it correctly, the CD medium uses 16-bit native files, so no choice of FLAC or other format is going to make it sound as good (if my ears can hear the difference) as a 24-bit “DVD” quality file, either downloaded from a 24-bit source, or recorded from one of the “better than a CD” disc sources.
The guys who do scientific-blind [u]ABX Tests[/u] have pretty-much demonstrated that “CD quality” is better than human hearing. For example, if you take a high-resolution original and downsample to 16/44.1, you won’t hear a difference.** In fact, a good quality MP3 often sounds identical to the original (in a proper-blind listening test***).
Sometimes when you buy a high-resolution recording you’re getting a different master or different mix, or even a different recording, so it can sometimes sound better or “just different”.
as a 24-bit “DVD” quality file,
DVDs are either 16-bit 48kHz uncompressed stereo (or mono) or Dolby Digital (AC3) which is lossy compression 1-6 channel). Dolby Digital isn’t an integer format so it doesn’t have a bit-depth. Sometimes there is a choice between lossless (LPCM) stereo and Dolby 5.1. I’ll take the lossy surround sound every time! Some of the best sounding music I own is on 5.1 channel concert DVDs.
Technically, DVD supports uncompressed 24-bit audio, but there are some strange rules that say they can’t use it with the CSS copy protection. There is an oddball format called DVD-Audio that supports high resolution lossless audio but the discs are rare and most DVD players won’t play it. Blu-Ray also supports high-resolution lossless.
Since my digital music player has usually been a smartphone, and the source of my music was mainly CD (with some high quality tapes from vinyl still in there, thanks to Audacity)
Of course, analog vinyl & tape is nowhere near CD quality. The “resolution” is limited by the noise floor. There are usually frequency-response variations, and sometimes with records there is distortion.
I’ve only just recently moved up to a true DAP which can do justice to 24-bit lossless recordings.
Most phones are quite good (flat frequency response, no audible distortion, and no audible noise). But, sometimes headphone impedance can “interact” with the phone’s output impedance giving frequency response variations (this doesn’t happen if you plug your phone into your stereo system or powered speakers) and sometimes a DAP can go louder without distortion than the phone.
- In Audacity, you have to make sure [u]dither[/u] is turned-off if you want the audio “untouched”.
**The ABX software is available so you can scientifically compare different file formats yourself if you wan to. An ABX test comparing your phone to your DAP isn’t as simple. The devices have to level-matched, someone else has to the switching so you can be “blind”, and the switching has to be done without any switching-noise that might give-away which device is being used.
*** It also turns-out that you don’t need a super high-end stereo to hear compression artifacts. If you hear compression artifacts it’s more-related to the program material (some sounds are easier to compress than others) and your ability to hear compression artifacts.