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Looking for upgrade from Apple TV, would like to keep using iTunes and wifi

My wifi-based sound has never matched my dear departed Arcam Alpha 9 CD player.  I've read forum after forum but I don't see a simple solution.  One possibility is that an audible problem occurs when the bit rate is changed from the CD native 44.1 kHz bit rate to the more traditional 48 kHz.

Here is my wifi system: iMac (iTunes) -> wifi -> Apple TV -> optical TOS -> PS Audio Digital Link DAC. 

The 300GB of music has been ripped from CD and is stored using Apple Lossless compression.

Yes, I know it's a lot of Apple software and gear.  I want to keep the iMac and iTunes and the wifi link.  I like the playlist features of iTunes, including the Genius feature. 

The Apple TV comes with a remote control and I can access the iTunes playlists directly, using my TV as a monitor, even though the iMac is in a separate room.  Once the playlist is playing I turn off the TV.

I am an electrical engineer and I've even worked measuring jitter on serial bit streams.  I understand that converting from 44.1 kHz to 48 kHz will cause some sort of interpolation error whereas converting from 48 kHz to 96kHz can be done with no trouble.  However, the Apple TV outputs 48 kHz so the bit rate must have been changed somewhere along the chain.  My PS Audio DAC won't even lock to the native CD rate of 44.1 kHz.

Are there any suggestions for a wifi receiver and DAC that will match the sound of a good/great CD player?  The budget is about $600, with an upper limit of $1000.

Thanks
pmiguy
erik_squires
16,214 posts
 
The issue isn't just of finding the right "sample count" but also consider what happens with amplitude math. What do you do when your interpolated step is 1/3 of the way between the two bits?

To be honest, I don't like the idea of most ASRC's not because of the math but the algorithms. Schiit has a great white paper on this, about closed-form rate conversion. With an ASRC you give up (completely) on the idea of bit-perfect transcription in exchange for timing (jitter) improvements. Still, the Remedy does a very fine job, and from what I've read, is especially good with non-audiophile sources. That was certainly my experience with Internet Radio, but I did not try it with AppleTV.

I will also say that I upgraded my DAC and the improvements went away.

Best,


Erik
kijanki's avatar
kijanki
4,428 posts
 
I would like to add to comparison between PLL and reclocker that reclocker does not replace PLL but works in addition. Any timing imperfections left by reclocker will be further repaired by PLL.

Any upsampling DAC will reclock the data using a PLL generated clock. The PLL has natural jitter reduction. I’m not sure that adding another jitter reduction device would help much. Most jitter reduction circuits are probably just using PLL reclocking anyway.
Jitter reduction circuitry used in reclockers, like REMEDY, is not based on PLL but rather on Asynchronous Rate Converter (does not use PLL).  PLLs have limitations.  Since based on phase comparison they can actually amplify phase noise of the reference clock.  The best scheme IMHO, that is both bit perfect and performance limited only by the quality of the internal reference clock is Asynchronous USB DAC.
erik_squires
16,214 posts
 
By the way, I've never heard of a DAC that couldn't do 44.1. I think you need to find your original docs. :)

Best,


Erik
pmiguy OP
9 posts
 
I like the idea of Async USB.  Why rely on the computer to do the timing?  It's better to let the DAC do the timing. 

I'll see what I can do with my old Mac Mini and the DAC that I have.  Eventually I may be in the market for a USB to SPDIF convertor or a new DAC.  I may look at the Remedy solution also.

Thanks everyone for the quality discussion!
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