I thought about the whole concept converting lossy compression to lossless to “improve” the quality of the source and why some people have a hard time understanding why it just doesn’t work that way. So I decided to take a stab at an analogy here.

Say you are stuck taking notes on a lecture with a really tiny notepad. You have to omit details since you only have enough room for the main points (lossy compression). Later that week, you decide to transfer your notes onto a full size notepad which would have had enough room for all of the details of the lecture (lossless). However, copying the notes verbatim from the tiny notepad to the full size notepad just leaves you with your original abbreviated notes on a big full size notepad (converting from lossy to lossless).

So that is the analogy I came up with while listening to the pod cast. The differences in data compression schemes are very difficult to explain to people who have trouble with a mathematical explanation. Does anyone else have an analogy?

Even worse is, never convert from lossy to higher quality lossy. This will lead to even worse quality than the original file as in theory you will lose more data in the second conversion (depends on the codec and quality settings, but you should assume you’ll lose something unless you go to lossless).

It’s actually not theoretical. Every time you convert from one lossy format to any another lossy format (even just reencoding with the same lossy codec) will always leave you with a more degraded data than what you started with. It is referred to as generational loss.

Lossless codecs don’t suffer from generational loss.

I’m reminded of Beavis, FIRE! FIRE! FIRE! Must be something innate in males that makes all like stuff to blow up. Fun times.

R.I.P. Boombox.

Share a little story with you about a friend of mines boombox when I was a kid (Mid 80’s). We used to sample different types of music in order that we could make all the LED level meters light up, and we came upon a Jimi Hendrix tune from his Smash hits album (dont remember which, Foxy Lady maybe) and the lights would remain lit up like no other song we tried. Hendrix became a legend to all of us from that alone, and then I figured out he was legendary for other reasons.

I went to a move theater in Laughlin,Nv it was in the casino & they hade bar made`s serving cocktails during the move way cool experience, I think theater/lounge is the way to go.

Andrew, I say theoretical because it really depends on the codec. Imagine if you encode at 64kbps and then re-encode to 320kbps. There is so much data lost that depending on the codec you might not actually lose more data. Although likely you will lose a tiny bit, it all depends on how the compressions is done.

So that is what I mean by theoretical.

Hey Miked, your correct in that there is so great a data loss in the encoding of 64kbps that there wouldn’t be much audible loss in a re-encode to 320kbps. But there is always some loss when ever you re-encode using any lossy format.

Think of it this way, you start with CD quality PCM data, currently the best lossless codec will need a bit rate of about 700kbps to create an exact duplicate of the uncompressed PCM data. So when encode to 64kbps using a lossy codec your at the very least tossing out about 636kbps of data (If the psychoacoustics model is good the least audible parts of the signal are in that missing 636kbps). So now say we re-encode that lossy 64kbps file to lossy 320kbps? Well, the 64kbps file is first decoded back to CD bit rate PCM data. So now we have the greatly degraded signal in PCM and that is passed to an encoder which will encode it to a 320kbps file. But we just established that it takes about 700kbps to represent PCM exactly. That means that at least 380kbps of data are dumped during the second encode.

Since every re-encode cycle starts with the source file being decoded to uncompressed PCM. If the codec is lossy it has degrade the data even more.

I can understand why you can convert a lossy format to a lossless format – I guess my question was really why would Apple add this functionailty. It seems completely useless and a waste of time. The initial question I was looking for an answer on was – is the AAC lossless format equivalent to CD quality and the consensus seems to be positive. So, my efforts coverting all those CDs is not all for waste. I will still keep one library to sync my 16GB iTouch for portability and create a second high quality version for connecting to my receiver. Better get to work…lots to do. Thanks for the input.

That should be “can’t convert lossy to lossless”.

Don, sounds like you’ve got a handle on the AAC lossless codec. AAC lossless is absolutely identical to AAC. The only reason I can think of to re-encode from a lossy file to AAC lossless is if your player supports AAC lossless and doesn’t support whatever the lossy format is. However, if your using an Ipod and your lossy files were created in Itunes there is no reason that I can think of to re-encode them… unless you just really want to fill up that half empty hard drive you’ve got sitting there..

I would do exactly what your doing, keep your entire music collection in a lossless format. Whenever you want to move a song to your portable player use the lossless file as the source and create a second lossy compressed song for your Ipod. What is great about this is that you never need to look for the CD’s again, you can just cue up a few hundred songs to be transcoded and copied to your Ipod and come back in a few hours. No swapping disks.

The other great thing about storing your music in AAC lossless is that if you decide you like another lossless format better in the future you can say convert from AAC lossless to FLAC (lossless) with out loosing any quality. You could even transcode between lossless formats hundreds of times and you’ll still have a file that is identical to the CD quality uncompressed PCM.

In other words, rest assured that if you import your entire CD collection as AAC lossless it will be the last time you will ever have to go through that very very long process.

Onkyo 805 on Fire? oh wow