How to find out if a WAV has been generated from a MP3
Reply #8 – 2010-01-24 15:57:29
Glad that's useful. If your graphs look like my 3rd, one (with complete cutoff of frequencies above 16 khz) then they were definitely sourced from low-mid quality lossy audio.
note that in the spectral views I presented only show one channel because R and L channels are almost always equivalent in terms of frequency cutoff (unless the encoded music has major differences between R and L channel) and I can make the point easily enough with an image that takes up less space if I only show one channel. a few more comments: 1) the common cutoff around 16 khz is there for a reason, because most people can't hear above that frequency (especially when there's other music at lower frequencies going on - i.e., they may be able to hear a 16 khz tone, but not hear the difference in actual music when it is 16 khz lowpassed. Also, high-frequency stuff is disproportionately difficult to encode (uses a lot of bits) so there's more reason for wanting to lowpass. 2) fake lossless or fake high-quality mp3's (sourced from lower-quality compressed-audio files) are somewhat common. there are a number of different reasons/sources for this:
people trying to sell something that's not as high-quality as it actually is accidental error on the part of the original purveyor, whether individual or a record company in service of iTunes or Amazon or eMusic, ripping from a cd that itself was created from mp3 files users who mistakenly think that transcoding mp3's to lossless or a higher bitrate improves quality some may be record companies intentionally injecting lower-quality stuff into file-sharing networks as a disincentive for people to use such networks
Last Edit: 2010-01-24 16:01:00 by timcupery