lossyWAV 1.2.0 Development Thread
Reply #531 – 2009-08-29 20:03:04
The idea behind --limit <=15000 is like this: Let's first assume that we are at --standard quality. --limit 14500 makes sure that there is no audible noise in the range up to 14.5 kHz according to 2Bdecided's basic principle. A high value of bits-to-remove means that there's pretty much energy all up to 14.5 kHz. With pretty high energy near 14.5 kHz I consider noise in the 14.5 ... 16 kHz range is masked enough. Considering further our low sensitivity in this very high frequency range. On the other hand a low value of bits-to-remove means a good S/N ratio at whatever frequency. To me this is sufficiently plausible to do it like this especially as at the --standard quality level we can assume that we have a pretty large safety margin towards the transparency border. At the --portable quality level things aren't that clear as we are in the range of heuristics below 2Bdecided's basic principle. But we aren't at the very start of lossyWAV experience. --portable seems to have some small safety margin. That's why I decided for me to use a little bit of a more aggressive setting in line with these ideas. My motivation for these things comes also from the fact that this way I don't have to care about reencoding rather strongly lowpassed mp3 tracks after having modified them. So things just come together, and I like the results I listened to. May be you can look at it like this: Noise analysis has always been restricted to 16 kHz for good reason (at least as a default). What I'm doing right now is put the question on the 16 kHz. Why 16 kHz? In the end it's an arbitrary choice (though it's clear that it should be at very high frequency). I just prefer 15 kHz at the --portable quality level, and even less for the higher ones. The -s setting isn't necessarily touched by these considerations. I just found that the -s bitrate penalty is higher with a lower --limit. And allowing for not directly controlled noise in the 14.5 .... 16 kHz area is in line with reducing the overall noise shift towards higher frequencies. But it's not a necessary conclusion.