.mp3 or .zip file directly from their server (right-click, save as). These files are often recorded at 22 kHz mono—low, but unrecompressed, which is as "better" as you will get for ATC audio.If you clarify exactly which recording you want (song, podcast mention, interview, or TV performance) and whether you want a free source or a paid high-quality one, I can give you the exact legal source.
Many free sites simply upscale low-quality YouTube audio, which doesn't actually improve the sound—it just takes up more space.
: You can buy the single or stream it as part of a subscription.