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Bit-perfect digital out


peter73
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Hi,

 

Did anyone tested any of the existing media players for bit-perfect output through their digital out?

 

Apart from Logitech/SlimDevices all other manufacturers provide no information on that matter.

 

I guess HDCD wav or flac and HDCD capable dac would be enough to test - has anyone done it with any of the currently available media players such as WDTV, Philips Streamium, Teac's etc.

 

Any information, references and in particular - personal experience will be much appreciated, as there is no much info on this on the net.

 

Thank you,

Peter

 

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All networked players should be bit-perfect with the exception of Apple TV and AirPort express, because Apple compresses the datastream to ALAC before transmitting. Sonos is still bit-perfect, but changes the data to 24/44.1, which is beneficial.

 

Steve N.

Empirical Audio

 

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I've read in another forum that one of the most recent and popular players - WDTV is applying gain even through the digital out. Upsampling to 48kHz is also quite common in pc audio and this is not beneficial, especially if the dac is doing some upsampling too (as does mine - Benchmark).

 

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All networked players should be bit-perfect with the exception of Apple TV and AirPort express, because Apple compresses the datastream to ALAC before transmitting. Sonos is still bit-perfect, but changes the data to 24/44.1, which is beneficial.

 

ALAC stands for (and is) Apple Lossless Audio Codec. Difficult to see how this could not be bit-perfect as it is lossless!! So the statement "compresses the datastream to ALAC" is misleading. Yes - if the source file is WAV the data is compressed but absolutely no information is lost because ... errr ... it is lossless.

 

My understanding that over wireless Apple always uses 16/44.1 so any higher resolution material will not be bit perfect but any 16/4.1 material will be as Chris has just confirmed in previous reply.

 

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"So the statement "compresses the datastream to ALAC" is misleading."

 

It's not misleading, its the facts. It does compress the data, and it must be uncompressed at the end-point device. ALAC does give perfect data compares, but there is more to the data than the data alone. There is also control information and the way that the S/W handles the data. This is I believe why systems that bypass the S/W audio stacks and use simpler data representations sound better, such as the Amarra system.

 

How do you explain the fact that the latest iTunes S/W download when ripping ALAC sounds better on playback than previous versions of iTunes, which also had bit-perfect ALAC data?

 

Bit-perfect refers to native rate files being delivered at native rate without modification.

 

Steve N.

Empirical Audio

 

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I have noticed that the more processing the PC has to do, the worse the sound is. Maybe the new iTunes is more effective in transcoding ALAC and causes less strain to the CPU and that's why the sound is better. In fact the same applies for cd recording with pc drives - a lot of processes running usually means worse sounding cd-r. Probably it has something to do with the fact that all devices in the pc are usually fed from the same PSU and the variance caused by load results in jitter.

 

Anyway, all of the above does not apply in case the jitter is removed at the DAC stage.

 

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"Bit-perfect refers to native rate files being delivered at native rate without modification."

 

Exactly Steve. In my opinion bit perfect is only the beginning, but it's an absolutely necessary beginning. Without bit perfection we are polishing turds.

 

Founder of Audiophile Style

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Steve,

 

How do you explain the fact that the latest iTunes S/W download when ripping ALAC sounds better on playback than previous versions of iTunes, which also had bit-perfect ALAC data?

 

It is well known that any lossless use will not sound as good as a flat PCM file like AIFF or WAV. Apple originally did all the ALAC work with the Ultivec engine in the Gx series processors. I made Apple aware as others had that the Lossless did not sound as good as the same file in AIFF. They changed the library functions for iTunes and now it sounds closer to AIFF.

 

Just in the same way that FLAC does not sound as good as WAV on a PC.

 

Chris is totally right about the bit perfect thing it is the place to start then everything else is gravy. We are running some tests now to determine why lossless seems to change the character of sound on high end systems.

 

But Steve I don't think Airtunes is ALAC. I have seen the source code to this stuff and I don't remember that at all. It is however at this point limited to 16/44.1 which iTunes will resample to this before sending it off to any device. However local file storage on the AppleTV can go higher, though I have not tried that in a while.

 

Thanks

Gordon

 

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"But Steve I don't think Airtunes is ALAC. I have seen the source code to this stuff and I don't remember that at all. It is however at this point limited to 16/44.1 which iTunes will resample to this before sending it off to any device."

 

Gordon - I'm pretty sure it is ALAC, however iTunes from a PC and iTunes from a Mac may actually be different transmission formats. iTunes over a wired ethernet may also be different. Some may be compressed, others not, and some may be 24/44.1 and others 16/44.1. Listening tests recently done at Arizona audiophile society demonstrated that the sound quality was much better when the same iTunes ripped ALAC file was streamed wirelessly from a Mac to an AirPort Express compared to PC to an AirPort Express. Definitely something fishy going on here.....

 

It would not surprise me if Apple somehow intentionally "crippled" the iTunes WiFi from a PC.

 

Speaking of Apple TV, at this meet did a similar experiment, this time playing wireless from the Mac to the ATV and then "syncing" the file so that it was on the local disk. Everyone agreed that the ATV local disk file sounded a lot better than streaming it WiFi. I was not there BTW, just reporting the anecdotal evidence.

 

Steve N.

Empirical Audio

 

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Steve,

 

Airtunes is the same all around. If it's ALAC then it's the same on all fronts. I will ask the guys at Rogue audio they write drivers and emulators for Airtunes. It is only 16/44.1 so any format other than that will be resampled to fit the 16/44.1 used to stream. There is talk of moving this up now that the "N" series is being used by all the macs and most newer PC.

 

Streaming is never going to sound as good as local connection. There is allot of people trying to locate their computers elsewhere but really that is not a healthy solution to getting better sound.

 

Steve it's simply silly to think Apple would cripple the "PC" version. They have tons of PC users and all the source code is pretty much identical as no computer company would want 2 sets of source code for a project that big.

 

Thanks

Gordon

 

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  • 2 weeks later...

I have been AB testing Apple TV against a number of CD transports of sufficient quality. The CD transports are using the same optical cable as the Apple TV and going into the same DAC. The Apple TV simply reveals more sound especially the quieter sounds normally somewhat lost in the background. While ATV sounds good to me, it also sounds like it's achieving it's results through dynamic range compression, making some background sounds more noticeable than other transports. I am using ALAC streaming to the ATV rather than stored locally. The other rather interesting thing that happens is that the layering of sound actually appears to be different. Comparing the two on some tracks gives a very different interpretation of the same song. Perhaps this is a result of it being in ALAC format? Lossless should be lossless, so I find that very confusing. If I stream AIFF and it transcodes to ALAC on the fly than it should sound the same as an ALAC file (which it seems to for me). If storing an AIFF locally however sounds better, than perhaps there is something fishy with ALAC. The device also supports video so perhaps they do implement some form of dynamic range compression to aid in movie playback and only apply to specific formats? At any rate, it does sound different and given that ALAC is supposed to be lossless, it shouldn't. I'm using a Windows XP box to stream from. The idea that it could be different if using a Mac is also quite confusing. I second the comment above, "something fishy is going on here...".

 

Mike

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"How do you explain the fact that the latest iTunes S/W download when ripping ALAC sounds better on playback than previous versions of iTunes, which also had bit-perfect ALAC data?"

 

Do you have data/evidence to suggest that this is indeed a fact rather than just a false perception on your account?

 

It isn't beneficial to the users here to spread potentially misleading information, especially when users are attempting to make a product buying decision.

 

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reedermw, interesting observations.

 

Can someone explain exactly what Apple TV is? For example, is it a router with special features? You know, I looked at the Apple web site, but was still left confused.

 

2013 MacBook Pro Retina -> {Pure Music | Audirvana} -> {Dragonfly Red v.1} -> AKG K-702 or Sennheiser HD650 headphones.

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The Apple TV is basically an iPod for your hifi rig. It has either 40gb or 160gb of storage that you can sync content to from iTunes running on another computer. Additionally, you can share your iTunes library and the Apple TV will browse and stream the content without having to download any of it. This works exactly like shared iTunes libraries between two computers in your house.

 

Mike

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Has anyone tried syncing hi-res audio to an Apple TV via ethernet and then playing back off the hard drive? I am wondering if it is the output that is limited to 16/44.1 or the wireless input. Or maybe its because there just is no midi software available to change to 24/96 as you do on the MAC? I am wondering if this constraint is just a software constraint and therefore correctable with another release of ATV software.

 

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I performed a simple test tonight that you can easily recreate in your own setup to confirm it. I ripped a track from Keiko Matsui (especially well recorded redbook audio CD's) in WAV, then in AIFF and finally in ALAC. All 3 are lossless formats so you can rip to one like AIFF then change the import setting to a new format, right click on the track and select "Convert to ...", repeat and rinse for the other formats. I am streaming from iTunes 8.1.1 running on a Windows XP box to the Apple TV using a wired (no WiFi) connection. To make matters easier, I renamed the track title of each song by appending (AIFF), (ALAC) or (WAV) to it so I would know what I was playing back on the Apple TV.

 

The AIFF and WAV files sounded identical and also matched both CD transports that I have. The ALAC file however sounded different. The overall tonal balance was brighter/higher almost like the entire recording was shifted up one octave in frequency. The dynamic range also seemed about 10db more narrow making softer sounds that would normally be well in the background more forward and apparent. The recording in general took on a brighter more detailed slightly louder presentation. The affect of this change varies greatly from track to track and may not be noticeable on some recordings. Keiko Matsui's albums are well recorded and never sound bad even when altered by the ALAC decoder on the Apple TV but while they seem to reveal more detail they also seem to lack some emotional impact at the same time.

 

My results have convinced me that the ALAC decoder in the Apple TV software is different than AIFF and WAV. This leaves me in somewhat of a quandary because I was hoping to store my library in ALAC format but now I'm inclined to put it in AIFF. AIFF is basically WAV with tags that can be used for indexing. WAV in won't work for me because while iTunes will record the info in it's database, there are no tags stored in the files so if I ever have to rebuild my library, it won't be tagged.

 

I don't think the above results would vary based on the OS that hosts iTunes. I don't have a Mac in the house at the moment to prove it but I believe that the ALAC decoder and settings are embedded in the software running on the Apple TV with the shared iTunes library being little more than a file share over Apple's Bonjour peer-to-peer protocol. Imagine the Apple TV as nothing more than a stripped down Mac running OS X and iTunes and you get pretty close.

 

So you guys using Apple TV's in your high end setups--are you using AIFF then? I think the Apple TV playing back AIFF is slightly better than either of my two CD transports perhaps due to less-than-perfect error correction required by CD playback. So the Apple TV bests a $2400 CD transport so I'd say it's a pretty good bargain. Still I'm not crazy about converting all my ALAC files back to AIFF.

 

Maybe Apple will fix this for us audio geeks.

 

Mike

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I can only comment on the Squeeze but, for me, there is a definite difference between uncompressed and lossless. I've had my unit for a couple of weeks now and have tried most format variations. The difference is not large, by any means, but it is there. Generally, lossless formats lose some leading edge definition - those little pre-note finger noises on acoustic bass, that sort of thing - and impact in the lower registers. None of this is earth-shattering and, for me, it comes down to the choice of whether or not I want decent file tagging, but in absolute terms the difference is there.

 

Supported lossless formats are decoded within the Squeezebox Receiver - after wireless transmission - and non-native formats (i.e. ALAC) are recoded by Squeezecentre prior to wireless transmission. PCM streams do not go through any decoding/recoding process at all and I can only assume that it is this fact that causes the perceived difference in sound quality.

 

I should mention that I have always preferred the sound of uncompressed audio to any lossless format I have tried, in all the different delivery systems I have tried. This may mean that I actually do hear a difference, or it may mean that I am both accomplished and consistent at fooling myself! Either way it doesn't matter much. I can live without tagging and I can't live happily with lossless.

 

Hope this helps.

 

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I have iTunes on a Mac and an Airport Express. I also have a Windows XP machine with which I experimented with Itunes as well.

 

1st off, iTunes on the Mac and PC are completely different animals. I don't think it is all Apple's fault. iTunes on the PC installs with Quicktime because iTunes uses Quicktime as its audio driver. Unfortunately, Quicktime on windows (well, last time I used it anyway) had no way to bypass the kernel mixer in Windows XP. This means that for most 16/44.1 music, it was usually resampled up to 48 then back to 44.1 on Windows XP.

 

As an experiement for you iTunes on Windows XP users, RIP your CD into iTunes at 48 Khz sample rate. I bet you your music will sound way better because the kernel mixer, seeing 48Khz data, has no need to resample, or is likely to resample less often.

 

iTunes on a Mac, as you all know, is different. First, Mac OS X has a default sample rate of 44.1. Secondly, iTunes on the Mac uses the OS to drive its audio, not quicktime, as is exemplified by adjusting Audio Midi.

 

So iTunes on Windows XP may be inferior because Apple did not want to have pay license fees for other parts of the Windows OS from Microsoft. A perfect example of this is Winamp. Did you guys ever notice how WInamp 2 sounded great but Winamp 5 wasn't quite the same? When looking at the version history of Winamp, Microsoft threatened the Winamp creators to stop using the built in audio engine of Windows, so with Winamp versions after 2, Winamp used its own audio engine.

 

Now, all these observation were made with and Airport express. The AppleTV may not be the same, but there will probably be alot of similarities.

 

Oh, and the Airport Express, whether it is wireless or wired, only works with 16/44.1 data. Mine is wired and 44.1 is all it can deal with.

 

Hope this helps.

 

CD

 

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Interesting comment. The post above where they discovered that a file stored locally on the ATV sounded better than streaming may due to a test where they were using the ATV as an AirTunes receiver (push rather than pull) and if the file were being played by iTunes on XP that could account for the differences. A file stored locally on the ATV should be played back by the software on the ATV (OS X). It would be interesting to know if the test referred to in the previous post was done in this fashion or not. I have shared my iTunes lib on the XP box and access it from the ATV as "Shared Music" (pull). I believe this still has the ATV player decoding the file and thus bypassing the XP KMixer but then I'm not exactly sure how the data is being transmitted. Hopefully they don't run it through the QuickTime engine on the box sharing the lib. I'm not sure how to even test this. I will say that the sound quality of an AIFF being streamed down to an ATV from iTunes running on an XP box (as "Shared Music") is as good or better than a good CD transport. So this may be an advantage that ATV has over AE if one is using XP.

 

Mike

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Hi Gordon,

could you please let us know when Apple would have "changed the library functions for iTunes" so that "now it sounds closer to AIFF"?

From what version of iTunes the supposed change appeared?

 

Thanx!

 

Arin

 

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