Apple TV Audio Quality

As I understand it:

When streaming from your Mac over AirTunes link to AppleTV, the Mac will convert everything to to Apple Lossless on the fly.

However, when playing direct from the Apple TVs hard drive, the audio is not converted to lossless.

Converting to lossless over AirTunes helps reduce network usage, but there is no need to do this conversion inside the Apple TV when playing direct from the internal drive.

In either case (in theory) audio quality is unaffected.

Welcome to the  Discussion Forums.

Apple lossless is compressed. To be honest I'm not actually sure what the tv does with it, but suspect since not all third party audio equipment is able to decode it that the tv decodes it itself before output.

For CD's which you have converted this is likely to mean that your audio is output as PCM stereo, which essentially means no loss since all it's doing is decompressing the files you send it.

However AL can support 24 bit audio and multichannel audio, so my suspicion is that this is also output as PCM stereo (16/48), which would suggest that in such cases there is a loss off quality/feature.

Bottom line is I believe for your CD's the audio will retain it's quality.

Apple Lossless is 'Packed' more than it is compressed. The data is packed in a way more akin to a .Zip or .Sit file - ie there is no Psycho-Acoustic compression like there would be with an MP3 or less-than lossless AAC file.

So in terms of audio waveforms, nothing is thrown away when 'packing' the file losslessly which is where the term lossless comes from.

So, to re-iterate, the OP's thinking is correct in terms of audio quality being retained when using Apple Lossless. The Mac will convert (on the fly) anything that isn't Apple Lossless already into Apple Lossless as it streams via Airtunes.

I'm not sure what happens with Hi-Res Audio, but I suspect that for the purposes of streaming via Airtunes, these would be down-converted to a 16/44.1 variant of Apple Lossless. So, in essence the only potential area for a quality loss is when using hi-res audio files. I haven't really looked into this though.

The Apple TV, playing files directly, will not convert any 16/44.1 files to lossless and will pass audio 'as is'. So any WAVs or AIFs will not be losslessly packed which saves the poor old Apple TV from working too hard.

The main part to remember is basically where the audio is originating from:

Streamed over Airtunes: The Mac will convert to lossless and send the lossless stream to Apple TV, Apple TV will decode lossless stream. = SAVES NETWORK BANDWIDTH

Played Direct from Apple TV internal drive: No re-encoding of format, just direct decoding of whatever format files is stored in. = SAVES APPLE TV PROCESSING POWER

Message was edited by: Easybourne

Message was edited by: Easybourne

I think we are essentially saying the same thing, or at least when it comes to the bottom line.

I believe we have differing interpretations though when it comes to AL. AL is compressed and indeed information is thrown away and reconstructed upon decompression through predictive algorithms. The difference between lossy and lossless compression being that lossy compression results in an approximate reconstruction of the original data, whereas lossless reconstruction results in an exact reconstruction.

Easybourne wrote:
Apple Lossless is 'Packed' more than it is compressed.

Put it another way it's losslessly compressed as opposed to the lossy compression of MP3 etc.

AppleTV's output over toslink is limited to 44.1kHz 16 bit for stereo audio. While you can play higher quality lossless files they are downconverted to 44.1/16bit which is a nuisance if you have 24bit depth files or higher sample rate audio purchases.

There have been a few threads on this previously.

If your music is from CD then it is presumably 16bit 44.1 kHz Apple lossless.

If you sync/stream this to AppleTV it should playback unadulterated over Toslink as linear PCM audio with the same characteristics.

If however you stream using Airtunes in iTunes using AppleTv as a speaker, while you should get 16bit 44.1kHz out, any effects eg equaliser/enhancement you add in iTunes may degrade the original audio.

As I don't know the exact coding of the audio transmission I can't say that Airtunes audio playback is not altered in any way.

In fact I've often felt myself that a file played over Airtunes sounds different to the one synced to AppleTV - try it and see.

All stereo audio in theory gets output as PCM and I believe that it all gets down/upsampled to 16bit 44.1 kHz - if you playback a compressed MP3 or AAC file it also gets output as linear PCM, i.e. converted in the AppleTV, as most receivers/DSPs don't understand MP3/AAC streams over toslink.

SteveSydney wrote:
I now wish I had bought the Apple TV instead of the MacMini (just sold on ebay) as the Apple TV is far less of a hassle to operate.

Capaho won't be happy to hear that !