I am considering using the Apple TV as a way to store a meaningful portion of my CD collection so I can play them on my home stereo without the hassle of CDs and with the benefit of the iTunes UI. My problem is that the bitrate on my Mac's iTunes collection is typically 192 or 256, and through burning music at that resolution onto a CD and playing on my home stereo, I know this is discernably worse than CD quality. I could store all my music in lossless format on my Mac, but my problem there is that I would be able to store a lot less music on my iPod. With a 160GB Apple TV, this wouldn't seem to be an issue. My question then is two-fold. Does anyone have suggestions on how I could store higher-bitrate music on Apple TV than what I'd like to be syncing to my iPod, and what is the most efficient way to get that music onto the Apple TV in the first place? Thanks in advance for any suggestions.
I want to preface this by saying that I'm speaking as someone who has professionally recorded, mixed and mastered CD audio as well as Dolby Digital soundtracks that meet the fidelity criteria of Dolby Laboratories in order to qualify for usage of their logos and trademarks.
Ok, aside from the fact that 128 Kbps is acoustically transparent to 16-bit LPCM according to SMPTE and AES... and the fact that 16-bit LPCM is itself far from pristine quality...
I ran some SNMP monitoring on AirPort Extreme and found that the bitstream sent when using AppleTV as remote speakers in AirTunes mode doesn't differ much from 128 Kbps AAC to 24-bit Linear PCM.
However, when using AppleTV, the bitrates vary in a manner correlated with the bitstream of the source. For example, a 256 Kbps AAC file generates throughput of around 288 Kbps. A 16-bit LPCM bitstream generates throughput of around 1712 Kbps (16-bit LPCM @ 44.1kHz is 1411 Kbps), and a 24-bit LPCM bitstream (2308 Kbps) generates a throughput in AirPort Extreme of around 2560 Kbps.
However, no matter what the source, when it reaches AppleTV, it is reconstructed as 16-bit, 44.1 Kbps LPCM, regardless, before making its way to a receiver.
What this tells me is two things:
1. Any bitrate file is going to be reconstructed as 16-bit LPCM, and considering the fact that AES and SMPTE engineers have in actual scientific studies found 128 Kbps AAC transparent to the source (regardless of purely anecdotal "evidence" layperson "audiophiles" repeatedly fool themselves into believing), there is no additional discernible benefit gained by encoding in Apple Lossless (AAC VBR). It's all going to be reconstructed as 16-bit LPCM. If we were comparing MP3 that would be a different story, but unlike MP3, AAC is a perceptual encoding schema that mitigates a great deal of unnecessary data using techniques similar to ATPX-100, ADPCM and AC-3.
2. The only method for actually achieving adequate bitstreams in real time from the source is to sync or stream from AppleTV, and not to put AppleTV in Remote speaker mode. This limits your options for organization because you will have to store the music on a drive linked to a PC/Mac running iTunes.
You could either use large internal storage on the machine you're streaming from, or use network-based storage if it's linkable to iTunes in the preferences pane... but you can't get around the fact that either you'll have to sync the same files to your iPod or encode secondary files at lower bitrates to iPod. However, if I'm not mistaken isn't there an option to instruct iTunes to convert high-bitrate files to lower-bitrate files on the iPod by on-the-fly transcoding during sync? Or is that only an option for the iPod Shuffle?
Frankly, if you do not possess a library consisting of 24-bit Linear PCM audio, it's not worth the extra storage to encode anything as lossless or uncompressed 16-bit LPCM. CD audio is dithered and limited to 65,536 amplitude values per quantization interval and at 128 Kbps, AAC is more than capable of delivering the same amplitude resolution, dynamic range and frequency response (when the sample rate is left at or above 2x the Nyquist rate). I have a lot of 24-bit LPCM and I leave that uncompressed, everything else I encode between 128 to 256 Kbps AAC.