So I hear a lot of talk about transcoding around here. People say lossy to lossy conversion is the work of the devil. Now the logic behind it is sound, you could be compounding artifacts on top of each other, but is it audible?
I found a song with some decent high frequency content. "Veronika's Dream" by Floex. Here's the spectogram:
I marked the clip I took of it in red, and circled a part that I thought should be particularly susceptible to artifacts.
I took a wav of this file and converted to 320kbps mp3. Then I converted it to 320kbps AAC. Then back to mp3. I did this a bunch of times. Probably over 30. Then I converted back to wav. Then back to mp3. Did this about 10 times.
Here is the download for the source: http://www.mediafire.com/?rk2d4s0edb235dc
Here are the 320kbps encoded files. One is a plain old 320kbps file. Another is transcoded between aac and mp3 a bunch. A third is that second file but converted back and forth between wav a bunch. NOTE: These files are not volume matched. dbpoweramp is not cooperating with me. If you would like to claim you can hear a difference, please provide an ABX log WITH replaygain enabled.
320kbps transcoding (Click to show)
Clean(only converted from wav): http://www.mediafire.com/download.php?opc9md3239h4amt
Dirty(transcoded several times between mp3 and aac): http://www.mediafire.com/download.php?rkfjwpprlbyu7tq
Extra dirty(second file with extra conversions between mp3 and wav): http://www.mediafire.com/download.php?5e2ywtbxkh3etpa
Now I don't know about you guys, but that's not too bad. But don't get me wrong, there is an effect. It is clearly shown in the spectograms.
Now this next part is particularly interesting. I tried the same with a 128kbps file just to display how transcoding is nasty. I recall doing it with another file just between wav and mp3 and it was ugly. But as I transcoded a good 20 or so times, I noticed there was no terrible distortion. Sure, it was there, but not like I remembered. So then I tried it between mp3 and wav, and it got nasty fast. Only after a few conversions some blatant ugly distortion came in. If somebody could explain this to me, that would be great. Why on earth would encoding between mp3 and wav repeatedly be worse than between mp3 and aac?
Anyways, here are the files. This one should be easy:
128kbps transcoding (Click to show)
Clean(only converted once from wav): http://www.mediafire.com/download.php?g25byxzbtn8rat6
Dirty(transcoded several times between mp3 and aac): http://www.mediafire.com/download.php?xym187byqb69nr9
Extra dirty(second file with extra conversions between mp3 and wav): http://www.mediafire.com/download.php?5x12lbbz0kts69c
Happy listening! Feel free to share your thoughts.
Edited by chewy4 - 2/27/13 at 4:19pm