airport express questions

Realremo - I think that Airport Express receives files in Apple Losless format. Keeping files stored in Apple Losless makes one conversion less.

Robr45 - That's what I meant, except I don't thing it goes back to MP3. If you start with MP3, for instance, Apple Lossles Compressor will uncompress it to some temporary format to compress again into APLL and then on receiving end it uncompresses to temporary format again to convert it to s/pdif format that goes out to toslink - no need to invoke MP3 compressor again. I'm not sure if it even needs to uncompress on receiving end - it might have algorithm converting APLL to s/pdif on the fly.

Rbstehno

If you take Jpeg and convert it to compressed TIFF(G3) and uncompress it later you won't get jpeg anymore but much larger file. That's exactly what is happening with MP3.

In order to be compressed into APLL it has to be decompressed first and MP3 format is lost forever. APPL file size will be larger than original MP3 but smaller than one compressed from original recording since MP3 lost part of the data.

Airport Express have no way of knowing what was original format used to convert to APLL. Everything looks the same and only amount of detail is different.

Perhaps you meant that Airport Express decompressed file has amount of data (quality) equivalent to original MP3.

"but it will always sound like mp3, those compressed/dropped out bits are gone forever." - I agree.

Jax2 - Stereophile tested digital output of Airptort Express and compared to original uncompressed file they sent from I tunes and they are bit for bit identical with 255ps of word jitter.

APLC does not reduce quality of MP3. There is no missing bits in MP3 (nothing to interpolate) - it has 16 bit resolution. Bits are not lost - the musical information is (simplified). In order to play MP3 it has to be uncompressed first. APLC is decompressing MP3 and then compressing it to APLC format to decompress it to uncompressed MP3 ready to send to s/pdif out. No missing bits.

I have no idea why APLC sounds different to some people. Time to process data has nothing to do with it since it goes thru output buffer. It is possible that people compare sound from different devices like CDP versus computer while not every device is "bit transparent". Some CDPs have digital volume control or some form of DSP processing. In addition Itunes might have volume control enabled as well as equalizer. Finally it might be placebo effect.

Jax2 - Itunes is not the best choice for ripping, I agree. I also agree that numbers published by Stereophile or other magazines are meaningless. I would even say that best tested devices have often the worst sound (there are reasons for that).

Stereophile reviews are pretty good but they tend to review only companies that advertise with them.

Rbstehno - I rip files into ALAC not only to save space but also to avoid additional operation (ALAC compression) that computer has to do in real time to send data to AE (it is not a dedicated server).