Well the first conversion from wav to mp3 removes inaudible information.Then convert that mp3 to wav, which is basically loss less, right?Now the second conversion to mp3 should try to remove the same inaudible information we already removed the first time and no more, therefore the second mp3 should be bit for bit the same, right?
theoretically this could work this way. (second encode will try to "remove already removed information", just like attempt to delete file twice doesn't result in deleting 2 files). but practically, none lossy codec I know works this way. reencoding/transcoding always results in quality loss, because psychoacoustic masking "isn't perfect" and will cause more and more degradations. this is the whole point of using lossless codecs for archiving.
original wav => mp3 =lossy
mp3 => wav = lossless but not better quality than the mp3 file
that decoded wav => mp3 again = a lossy progress again
Codec does not remove anything. It rounds some values to be able to store them in less bits then original ones.
How can the codec remove what has already been removed?
It doesn't care if the WAV was previously MP3 encoded.
QuoteCodec does not remove anything. It rounds some values to be able to store them in less bits then original ones.Of course the psychacoustic model removes a lot!
that essential process in lossy compression is adding (quantisation noise) not removing...
If you record a CD into a cassette tape, then use the tape to master a new CD, does it sound the same as the original? If you later copy this second CD to a new tape, does it sound the same as the first tape? Same answer.Thats why we call those "Lossy". Same happens when you do VHS copy from a VHS source. VHS stores in much lower bandwidth than that used in the external transport cables (made to connect to a TV, which needs the higher bandwidth).
In the jpeg analogy, lets say we can only see 100 colors.We reduce the picture down to the 100 we can see. (like wav to mp3)Then we convert it back to full color (like mp3 to wav)Then we go back to the 100 colors (like wav back to mp3)In theory it would be the exact same as the first reduction to 100 colors.
But reducing the amount of colors is only ONE of the JPEG artifactsThere's also smoothing, detail loss, blockiness...Same thing is for audio. It's not only reducing the amount of "sounds". It reduces details, introduces pre-echo and other artifacts...
but the point is not to explain jpegs or mp3.It is to show how a lossy format can possbily not get progressivly worse upon repeated encodings and decoding.
for the same reason MP3's could even sound better than the origin CD...He told me that MP3 decoding is a completely different process than WAV (CD-ROM) or Redbook (CD music) decoding, which results in a more "organic" sound. He went on to say that MP3s with sampling rates in the 300+ kbps range can sound better than CD. it made me think I was listening to quality tube gear. That is a tough feat to pull off: "smooth detail." MP3 is a reflection of CD in the sense that some recordings are imbued with much more ambiance and dimensionality than others. On some MP3s, I could actually hear beyond the soundstage and into the ambiance of the recording venue, which, as I said, is my hi-fi Holy Grail.Other hi-fi attributes were also present on MP3 via the HeadRoom: dynamic punch when called for, and a tight bass perhaps in the 30-hz range from a particular synth-based recording.
I perceived the decay of plucked notes on an acoustic guitar and the startling snap of snare drum shots, and could even distinguish among the drums used. And there was no harshness whatsoever. (I typically listen at a sampling rate of 128 kbps, which is a pretty good comprise between compression and not).
In terms of its smoothness, it made me think I was listening to quality tube gear. That is a tough feat to pull off: "smooth detail."