Airplay music streaming and internal DAC bypass

I had the same problem and I didn't notice it until I bought better speakers. I did an A/B test as you said and unfortunately the degrading of the sound is very noticeable. You hear a "bit reduction" effect coming out from the tweeters!

hhmmm DAC mean digital to analog converter

the Apple TV have 2 means of outputting audio one being hdmi the other being optical

both these audio outputs formats are digital so the Apple TV does not contain a DAC because it does not output analog signals

I AM very interested in this as I have the same setup. How come you know by the volumecontrol that a conversion has happened?

Airplay Mirroring is a bad way to preserve audio and video quality. It doesn't.

Simple Airplay using the AppleTV as a speaker for iTunes allows you to adjust playback volume and as you noted equaliser settings etc on the computer which as you say will to some extent degrade quality. I highly doubt there's a D to A then A to D conversion on the computer, rather tyhe adjustments will be made to the audio in the digital domain and an altered digital stream sent to AppleTV.

The best way to bypass these things is to play directly from Computers via Home Sharing which will pull the unaltered audio stream from iTunes - unfortunately however AppleTV 2 and 3 resample to 48 kHz on output - you may or may not notice.

In essence AppleTV is a cheap consumer device with little thought for the audiophile or videophile (no '24fps' output when the iTunes movies are encoded at near 24fps).

Max_Ram wrote:

Ok understood, thank you very much.

So if the Apple TV is downsampling my files there will still be some digtal manipultation and no bit perfect signal will be sent to my external DAC. The only way to achieve optimal sound quality and a bit perfect output is to plug the computer directly with USB cable, am I right

I've not updated to the most recent AppleTV firmware and iTunes is always changing, but it used to be the case that say a lossless CD rip was added to iTunes, i.e. 16 bit 44.1 kHz, the AppleTV would then output at 16 bit 48 kHz - I am assuming the upscaling here is done in AppleTV but I'd prefer the original unadulterated bitstream to go to an amp or standalone DAC.

I don't have many higher than CD quality audio files as the selection is limited in the UK, but I think when I last tested with a 24 bit 96 kHz album that again AppleTV output at 16 bit 48 kHz both downsampling and reducing bit depth. I must test again as I have probably replaced my old Yamaha Av processor with a Pioneer since then. In the last year I've gradually removed my separates from the AV rack and I'm amazed at how well the Pioneer does by comparison - not the same overall quality, but excellent detail and control. Undecided about putting the hi-fi separates back, as several components need some maintenance.

Max_Ram wrote:

Are there any hi-end devices out there able to manage a shared iTunes library (like the ATV 3 does) with bit perfect output?

And has the Airplay feature in some "audiophile grade" devices like NAD, Marantz, etc. the same behaviour?

I suspect you'll find many of the high-end audio devices use custom library software - they may not run with iTunes directly, but I suspect some will be able to access files stored in iTunes. The problem really is the AppleTV is not configurable to simply output what it is sent - I don't honestly know if for example iTunes downsamples hi def files before sending to AppleTV or if AppleTV does it internally.

In many ways it may not matter if AppleTV is not outputting as you want.

I think the problem with Airplay is that the technology is licensed from Apple for inclusion in those devices - from memory things like the first Zeppelin Air used to boast high-quality DACs but actually the Airplay stream that went to those devices was lower quality. I've not really tested any of these things for a while to be honest and am rather out of touch with current AV gear. Thinking about it I can use my Pioneer as an Airplay destination, but as you have noticed volume control/equaliser etc are active so the stream is not the original - must check on sample rate/bit depth though.

Airplay may or may not be capable of what you want now, but even if it isn't it may evolve to do so in the future. I suspect your best option will be to connect your Mac directly to the DAC if streaming won't work.

This is old and mentions some variably priced playback apps aimed at audiophiles:

http://www.headfonia.com/os-x-audio-players-amarra-audirvana-pure-music-fidelia- decibel-and-bitperfect/

BitPerfect is available in the AppStore - OS X removed some APIs for low level access to audio output some times ago - not sure if they are available again now.

Fidelia also in AppStore but has some in-app purchases.

Audirvana looked promising.

Not used any of these recently.

Amarra used to be very expensive.

In the past there have been several lively discussions here where people have moaned that AppleTV does not have a volume control - I have always argued that it is a 'source' device and volume etc should be controlled on the amp or TV as with conventional audio sources but many devices do have volume controls these days so consumers who like those features want them. They did actually add volume control to AppleTV 1 for stereo audio but you could disable it in Settings.

Here's some other links you may or may have not seen.

AccurateRip for trying to get bit perfect CD rips - I think in essence the feature generates a checksum to match your file against that of other people who've ripped the CD so you can have confidence it's worked properly. Personally iTunes is generally easier to do the job, and my CDs tend to be in good condition as I usually rip to iTunes then the CD goes into a box for storage!

http://www.accuraterip.com

X Lossless Decoder used to support it, and it can be an excellent toolkit for processing audio files and converting say FLAC to Apple lossless.

http://www.macupdate.com/app/mac/23430/x-lossless-decoder

(Can't find the developer's site link at the minute).

thanks for an informing discussion. Forgive me if it is a dumb question, but what is tyhe adjustment and what effect does it has on the output quality?

Sorry which bit are you referring to when you say 'adjustment' ?

Max_Ram wrote:

Alley_Cat wrote:

I've not updated to the most recent AppleTV firmware and iTunes is always changing, but it used to be the case that say a lossless CD rip was added to iTunes, i.e. 16 bit 44.1 kHz, the AppleTV would then output at 16 bit 48 kHz - I am assuming the upscaling here is done in AppleTV but I'd prefer the original unadulterated bitstream to go to an amp or standalone DAC.

I don't have many higher than CD quality files too, but I really want, as you said, the original untouched bistream to reach my hi-end DAC.

Are you sure that the Apple TV will do an upscaling for, say, an ACC 256Kbps 44.1 kHz iTunes suource file? I haven't got any DAC with display, so I can't check.

Scouring my Pioneer's manual I am struggling to find a way to display the PCM stream characteristics - for stereo audio AppleTV outputs linear PCM.

I am currently using 'Airplay' to push a 24 bit 88.2 kHz file to AppleTV over HDMI - the amp is showing PCM and it tells me in an audio menu that the sampling frequency is 48 kHz. So here the audio is being downsampled to 48 kHz. I can't tell if it's 16 bit or 24 bit unfortunately, though I suspect 16 bit.

Next using Computers>Music menus on AppleTV to pull the same file, the iTunes volume and equaliser are ignored as expected BUT the sample frequency is again shown as 48 kHz - does AppleTV get the 24 bit/88.2 kHz file and adjust it or does iTunes convert on the fly and just doesn't apply volume and other adjustments.

If I use Airplay to send the same audio to the Pioneer as a target Airplay speaker direct the sampling frequency is not even displayed!

Just switched to a 256 kbps 44.1 kHz iTunes purchased AAC audio file via Airplay to AppleTV over HDMI - sounds poor by comparison, but it's again showing as 48 kHz on the amp, so upsampled.

I need to dig my Mac Mini out - this was one reason I got one, in order to output the audio better over HDMI or optical.

Max_Ram wrote:

I don't have many higher than CD quality files too, but I really want, as you said, the original untouched bistream to reach my hi-end DAC.

Are you sure that the Apple TV will do an upscaling for, say, an ACC 256Kbps 44.1 kHz iTunes suource file? I haven't got any DAC with display, so I can't check.

As with many things audio related - perhaps the best thing to do would be just to do an A/B test - hook up the Mac directly to the DAC and listen then repeat using the AppleTV for playback from the Mac - all the specs/concerns about different rates/bit depths are only theoretically relevant - if as the listener you can tell the difference it's significant, if not it doesn't matter.