I always ask my clients to record or export their tracks in better than 44.1 kHz 16 bit resolution, preferably in 48 kHz 24 bits. A very common reaction to my suggestion is “why should I bother with this if the final master will be in CD audio format anyway?”. Here are the reasons why you should record audio in high resolution.
The quality of a digital audio recording is technically determined by the sampling rate and bit depth used during recording (we’re not speaking about mics, preamps, interfaces etc. now). If you want to reproduce an analogue sound source digitally whose maximum frequency ranges up to 20 kHz (the upper limit or human hearing), you’ll have to use a sampling rate of 40 kHz at least (see the Nyquist–Shannon sampling theorem for more info). Since no A/D converters are perfect 44.1 kHz was chosen as the standard in many aplications, including CD audio. This means that your A/D converter will capture 44,100 discrete samples from the continuous analogue signal per seconds.
Now let’s see bit depth. Bit depth can be referred to as the resolution of a discrete sample. The CD audio format can contain up to 16 bits of information per sample. This determines the maximum dynamic range and signal-to-noise ratio. In 16 bit audio this is theoretically 96 dB, in 24 bit audio it’s 144 dB. So when for example compression or equalization is applied during the mixing and mastering session you further limit the dynamic range and lose bits, i.e. you degrade audio quality.
A good way to demonstrate the negative side effects of this is to use an example of digital image processing.
I took this high resolution image:
First I applied some color and tone corrections on it (just like equalization in audio) then I applied a “cut out” filter which reduced the details with a nice character (similar to compression). Here’s the result:
What would’ve happened if the image were resized before applying the corrections and filters on it? Take a look at this picture:
Comparing it to the previous one you’ll find it blurred and less detailed. And that’s the point.
If you record audio in high resolution much more detail and transparency can be preserved during mixing and mastering. So when your song is converted to the lower resolution target format in the very last step you’ll lose much less from the sound quality than if it were recorded in CD audio format right in the beginning.