(4) Data Compression (mp3) and all that...

[kenja]

Hello John

This issue of lossy /lossless compression has risen it's head once more now I have started again (this time successfully) to use the latest SonicStage software to transfer tracks onto minidisc.

What concerns me now is this: If a wav file is burned to a cd it converts it to a cda file on the disc. Now if this file is then converted back to a wav file would there be any loss in either or both directions?

I ask because in the past I used to burn the wav audio files produced from midi onto CDs and then put them onto minidisc (the latter which of course is a lossy conversion). If I wanted to alter the track I would then import it from the CD into CoolEdit Pro as a wav file then save it again.

So I thought I would just get it clear as to what is actually happening here and whether any of it is detrimental.

Hope you can assist in this

Best regards

Ken

[JohnG]

Hi Ken,

Sorry for the delay in getting back to you on this. Other things ...

If the CD is in perfect condition then there should be no loss whatsoever. However, not all commercially produced CDs are in perfect condition despite the fact that you can see no blemishes on the surface. So, I use a utility called EAC. It stands for Exact Audio Copy, and uses all the tricks in the book to attempt to make sure the copy is exact (cda to wav), like reading multiple times and comparing the reads. Not all, in fact very few, other programs do this AFAIK.

Another factor is that cheap CD-Rs may deteriorate over time. I put important stuff on archive quality CDs. Another way is to burn the wav files into a data rather than an audio CD. A data disk puts extra checksums, parity etc. onto the disk to ensure perfect recall. These are not put onto audio CDs as they must stream the bits at high speed and don't have time to check every byte. You may occasionally hear a click from an audio CD.

So the answer is that cda format "should" be perfect, but isn't guaranteed to be so.
But the cda file when written should be an exact copy of the audio in a wav file. It's whether or not it can be successfully, perfectly read again that's the issue.

Any help?
JohnG.

[kenja]

Hi John

Thanks for the explanation on this it's very useful to know.

One other thing I have considered is whether saving a WAV file in it's original recorded (by me) condition or whether to ditch it once the wave is normalized.

I use "Group Waveform Normalize" routine in Cool Edit Pro and normalize to -9 dB and use hard limiting, which gives me a nice equal loudness to all my tracks. However it means that transient spikes and other loud bits get taken out. I had assumed that this would not make any difference to the track but would there be any reason to want to keep the original or is this being too picky?

Ken

[JohnG]

Hi Ken,

My own personal take on this is to keep the original. The processing can always be re-applied if necessary to recreate the "performance" track but if, for instance, you ever wanted to create a CD in the future, you might want a different version with more dynamics. My own approach is always to keep the original and throw away the processed version. More flexibility should I need it. Who knows what tomorrow will bring?

JohnG.

[JazzCat]

Just a quick note to kenja,
cda is not an audio format at all. It is a shortcut to the .wav audio file that is on the CD.
Taken from Wikipedia:

The .cda (Compact Disk Audio Track) is a small file that serves as a shortcut to the audio data for a track on a music CD. It does not contain audio data and is therefore not considered to be a proper audio file format.
=============

When you are 'converting' wave to cda, you aren't actually converting at all. You are just adding the shortcut file. Put a professionally recorded CD of your favorite band in your computer's CD . Open it with Windows Explorer or the Mac equivalent. Make sure to view as 'details' and notice the file size of the .cda file. You will see that it is only a 1 kb file.

[kenja]

Hi
Thank you for that insight, I have learned something new and very interesting. Funny though how the actual wav file doesn't show up then on a cd?
Ken