Bit-perfect digital out

[reedermw]

Here's a discussion of the new ALAC encoder: http://forums.ilounge.com/showthread.php?p=1326500

 

I performed a pretty interesting test tonight. I took one of my existing ALAC encoded files (ripped some time back with 8.0) and converted to AIFF using iTunes. The resulting AIFF file sounds correct and doesn't have any of the previous problems that I found with the ALAC version. This conversion was done with 8.1.1 of iTunes. And here is where it gets really weird, I converted this AIFF file back to ALAC using iTunes 8.1.1 and the resulting new ALAC file sounded perfect. I changed the track title of each by appending (ALAC) to the original and (ALAC2) to the newly encoded file so that I could easily identify both in Apple TV's interface. I can AB both of these files now and the older ALAC file sounds off and the new one sounds correct. Thinking that I had completely lost it, I re-ripped the CD again just to make sure that I wasn't hearing things (pun intended). I believe ALAC is now fixed in iTunes 8.1.1 and I think all I have to do is mass re-encode using iTunes to fix them up. So that's good news but, wow, what could possibly have changed? The file sizes and bit rates are different between the old and new. Perhaps it's header/tag data that controls the decoder that was changed rather than the PCM data itself?!?

 

I don't see how the compressed PCM data could be different. There have been many tests confirming bit perfect output. An HDCD rip that lights the HDCD decoder on a DAC/Receiver, etc. How else could I convert an old ALAC to an AIFF and have it sound correct and then convert that file to a new ALAC and have it fixed. This tells me that either the changes made in the new encoder are header/tag data that controls the decoder or all my ALAC files are not really/truely lossless and mass converting them in iTunes to the new ALAC will make them sound correct but they won't be the same as a re-rip. The thought of spending the next 6 months re-ripping all my CD's is unbearable so I'll not even consider it.

 

[audioengr]

"I don't see how the compressed PCM data could be different. There have been many tests confirming bit perfect output."

 

This is where the debates start and end-up beating the dead-dog.

 

There are evidently software/control issues with players and rippers that dont show-up in static bit-comparisons. I dont know how, but the differences are there.

 

Why do you think studios completely avoid FLAC and ALAC? They put tags on .wav files.

 

These lossless compressors only reduce the file size by 50% so why bother? Use AIFF.

 

Its really annoying that most of the downloads that you can get are FLAC or Windows compressed data.

 

Steve N.

Empirical Audio

 

[Nuke Yuler]

Its really annoying that most of the downloads that you can get are FLAC or Windows compressed data.

 

Assuming there are real quality issues with players playing compressed lossless formats, just turn them back into WAV and play them. Right? Sure.

 

There are a lot dead dogs getting beaten here in recent weeks. A lot of brand new people coming here and asking old questions. Nature of the beast, I suppose.

 

Steve, you're certainly contributing in many forums and writing things you've written many times. I appreciate your perspectives more than many but don't you get a little tired of 'beating dead dogs'? I've written probably less than 20 posts here and I'm seeing a lot of rehash to the point that I'd rather be playing with my gear than sifting through the forums.

 

- Rand

 

[Fyper]

 

- First of all bit perfect and lossless have little to do with each others:

Bit perfect refers to how the audio digital file is played and sent to the DAC. Bit perfect means that nothing (no bit) has been changed compared to the original digital audio file.

Lossless refers to compression algorythms which can compress (size) a computer file without any loss: when you decompress it is exactly the same as the original file. (like a zip file)

 

In other words: there can be no difference between a wav/aiff file and the flac/alac file created from it => once decompressed the Flac/Alac gives a file strictly identical to the original wav/aiff.

It is very easy to check if anything was lost: unzip the Flac/alac into wav/aiff and run a bit to bit comparison with the original file.

 

Then it is sent out of the player through the digital output to the DAC. At that stage and one can compare whether this PCM file is identical to the original PCM file : this is to check whether the player has modified the PCM file (this has nothing to do with the file format or lossless compression, it is about how the file is modified or not while going through the layers of the player to be transformed from Computer file to digital audio flow. if it is unchanged then it is bit perfect.

 

To explain it differently: take an MP3 file. This file is a compression from a PCM file and some data has been lost => not lossless.

Put this file through a player : if what goes out of the player is strcitly identical to the original MP3 file, it is bitperfect.

 

From a computer:

- It is said that Itune out of a Mac is bitperfect without further manipulation. (that means by the way that there is no way to improve it through any software : it can't be more perfect that perfect...)

It is very easy to check if a file is bit perfect: digitally recorded a file from the SPDIF/AES output of the computer/ausio server and run a bit to bit comparison with the original.

- However, as already said here, XP or Vista do temper with files. The only way to have bitperfect sound out of Windows is to use KS, ASIO or WASAPI (Vista) drivers. If you have a player and can install these drivers, you'll play bitperfect. It isn't possible to put these drivers with Itunes under Windows therefore Windows will temper and Itune won't be bitperfect.

However, similarly to a Squeezebox, if you use Airport Express, this will be bitperfect because Itune/Windows won't actually play the file, just zip it into an Alac format before Windows has any chance to change it, then send it to the AE which will unzip it into a perfect PCM file to be read by the DAC.

 

Hope this helps

 

[Codifus]

I should have mentioned that my bad expereicnce with iTunes on Windows was with a soundcard, and it clouded my trust in using itunes on windows with an airport express.

 

Now, in Windows, if itunes enables any digital audio manipulation, say the volume is set lower than 100%, EQ is turned on etc, say goodbye to bit perfect output. The same thing happens on the Mac as well, but with the Windows configuration of iTunes, the degradation tends to be more significant.

 

CD

 

 

 

 

[reedermw]

Nice explanation Fyper. That matches my understanding as well. Since I am using Windows XP as my iTunes/media server I have to be concerned about KMixer and it's altering of audio data. The Apple TV runs a stripped down version of OS X and I would hope it would play back files and output bit-perfect data. The lingering question for me is this--if I am using "shared music" mode on the Apple TV, does this mean that the Apple TV is just copying the ALAC file down and playing it back through it's own player/codecs? If so, then it should be bit perfect playback. If on the other hand, it's using QuickTime on the XP box to playback the ALAC file and sending the output to the ATV, then the output would not be bit perfect.

 

Am I safe to assume that since the ATV run OS X and has it's own player that it's outputting bit perfect data even though the data is coming from iTunes running on XP? The SqueezeBox on the other hand doesn't handle ALAC natively meaning that SqueezeCenter would have to be using QuickTime on XP to playback the file. So would I be correct that the output from the SqueezeBox where SqueezeCenter is running on XP would not be bit perfect. If so, it would seem that one would want to use FLAC on SqueezeBox and ALAC on ATV if lossless compression was desired as well as bit perfect output.

 

[reedermw]

>> "I've tested the Apple Airport Express and Apple TV.

>> Both are bit perfect via the digital output."

>>

>> __________________

>>

>> Chris Connaker

>>

>> Founder

>> Computer Audiophil

 

Chris,

 

Did you confirm using AIFF, WAV or ALAC files from the Apple TV?

 

 

[bottlerocket]

That was confusing information on XP and Itunes and ATV. I have XP, Itunes and ATV also. If I rip to AIFF or ALAC and sync to the ATV am I playing bit perfect music? Thanks.

 

Inching toward a Mac Mini ...

 

[Steve_S]

Just to add to the confusion, after a long night of PC versus Mac and testing several players and output methods, we ran across one very unexpected result. iTunes 8 sounded at least as good if not better on the PC, with all settings to default. This was especially surprising because iTunes uses the Windows kernal, which isn't regarded as being very good at accurate sound reproduction. Tweaking the Midi settings on the Mac made improvements beyond the sound quality of the PC with iTunes.

 

[Lowlands]

Trying to grasp the essence of the above (whilst attempting to dodge the beating the dead dog syndrome)..

 

Quote Steve: "Bit-perfect refers to native rate files being delivered at native rate without modification." Quote Chris: "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."

 

There is a lot of debate & questions on various aspects (OS, wireless streaming etc..) messing up a bit-perfect signal entering the DAC. There also seems to be a majority opinion / experience that a bit-perfect data signal comes in variaties that do NOT sound identical. That complies with the quotes from Steve & Chris.

 

Question: what comes after the 'beginning' of bit-perfectism; what else is there (in the digital signal domain...) that defines sound quality? Is that 'else' defined by the timing accuracy (jitter behaviour) of the digital signal in it's entirety, or are there other factors (or stuff we do not understand, but are just there..)?

 

Hans

 

[BobH]

Is that 'else' defined by the timing accuracy (jitter behaviour) of the digital signal in it's entirety, or are there other factors (or stuff we do not understand, but are just there..)?

 

FWIW, Yes! Where I'm at with this stuff is that some folks will say it's jitter, some will say it isn't, some will say whatever and others will argue. In the grand scheme of things what really matters, to us mortals, is what it sounds like. We've got to the stage now where you have to go tip-toeing around some answers because if you say something that cannot be verified, all hell breaks loose! From a science perspective that is fine and is as it should be. From the end-user perspective it doesn't help because if you think you hear a difference then it will affect your enjoyment of your system, one way or the other.

 

So the only practical thing left to do is to go with what sounds best and enjoy it! I've stopped worrying about the why's and wherefore's - I'll let the big guns sort it out amongst themselves. If I think that software A sounds better than software B, I'm happy to say so and let folks try it out for themselves and make up their own minds. That's what I do. Worrying about the 'how the hell can that be right' problem leads only to terrible headaches and adds to my general bewilderment.

 

I'm quite happy to accept that my ears are attached to a moron - too easily parted from his money - and that tomorrow I'll probably change my mind again and try something else. It is a hobby, after all! So, why one bit perfect stream should sound different to another is a complete mystery to me. The fact that, in my opinion, they can and do, on occasion, sound different, I find intriguing because it doesn't make any sense - but there's quite a lot in this little old world that makes no sense to me!! So that, really, is the essence of it. There's nothing there that can make a difference using known science and that dog gets soundly thrashed on a very regular basis, in every audio forum on the web.

 

Bottom line? I'm happy to allow myself the little luxury of putting science to one side when my ears tell me the impossible sounds better!

 

[Wavelength]

Gang,

 

Something more to ponder... We know that iTunes on the PC sounds better on Vista than XP. Sure that is simple since the KMIXER will be involved. But why is that if you skirt by the KMIXER (ASIO, Unmapping whatever) that Applications still sound better on Vista using Direct Sound than it does on XP?

 

I think there is basically a few parameters effecting everything here. Bit true, jitter, timing and noise pollution.

 

Thanks

Gordon

 

[BobH]

And thank you. I've never used Vista, myself, but certainly on XP I ended up preferring Foobar via DirectSound2, to MediaMonkey via WaveOut. I never did get on long-term with Asio, in any flavour.

 

I think you may well have a very good point - that all this stuff is interrelated and what we end up using is the combination that offers us the compromises we can live with. I'm just glad there are folks like your good self out there who seem to be able to cope with the headaches better than me!

 

[reedermw]

I spent months with both XP and Vista and can confirm that they sound quite different. I tried many different programs and drivers and ended up with a USB DAC to bypass the KMixer alltogether. Even so, I noticed a difference between XP and Vista. So the way that QuickTime works on Vista vs XP appears to be different. I don't have access to the source or the ambition to figure it out. I eventually moved to the Apple TV because it took all those variables out of the equation. The Apple TV runs OS X and the player is native to it. So assuming that one likes the sound that it produces, it buys a lot of flexibility on how the files are actually hosted. Since I work on computers for a living, my PC's around the house change frequently and I didn't want my audio setup to change every time changed the hosting box. The SB does the same thing if you are willing to use AIFF or FLAC. ALAC on SB is questionable since it uses QuickTime on the SqueezeCenter box to decode it, the resulting sound quality of an ALAC file played by a SB can be dependent on the OS hosting your files (I think). Since I would rather manage my lib with iTunes, it made my choice an easy one.

 

[reedermw]

Squeezebox streaming from SqueezeCenter DOES bypass the kmixer on Windows XP. For more info: http://www.avsforum.com/avs-vb/showthread.php?t=947502

 

[anm]

Hi,

I have been looking at this site for a couple of days now and seems like a perfect destination for those who want to play from their comps, or similar devices. This is the future! Though this site seems to be apple inclined (sometimes I just wonder if it is apple sponsored too), I would still like to ask about the WDTV. I do not have any mac computer, never had one. I just have one laptop but that is for office work. Can't put it as a dedicated one in there.

However, an HDD connected to WDTV seems like having best of everything, and in a budget. I do not need to run another dedicated server, or another PC to play media. All I need to rip my music using a comp and EAC (once in a while activity) download track info etc, copy it to the hdd and play off it.

Though this seems like the perfect plan, need to understand the perfectness of the bits. Can some guru share their measurements of wdtv when it comes to being bit perfect, not being resampled at 48k, usb noises, low/ high jitter etc.

It seems when in this thread people are saying apple airport is bit perfect, they actually mean bit perfect for a CD quality, and maybe not for higher resolutions like 24/96?

Please help. Thanks in advance!

 

regards

 

Edit: Another question, even in a bit perfect output, can data arrive with variable possible delays? So a file measured after file transfer is complete may be bit perfect, but during the transfer the bits played with music?

 

[anm]

I hope it's fine to bump after 5-6 days of no response. Seems it got buried under other threads :-)

 

[PeterSt]

I sure missed it. :-)

 

I have one, and the first question I want to ask you is : how would you think bit perfectness is going to be important while the WDTV doesn't have a digital out.

Or maybe yours has ? (or I overlooked mine)

 

So what it comes down to is that your question can only be about

 

a. bit perfect up to the loudspeakers of the TV

or

b. bit perfect up to the analogue out of the WDTV.

 

Well, both (to me) don't seem to do any good job were it for high quality audio playback.

 

Maybe ... just maybe there's a chance of your TV passing through SPDIF. Thus, go via HDMI to the TV, and from there digital out to a DAC. But then I wouldn't even know whether the output over HDMI is digital (I suppose so though).

 

Now, it seems obvious that you didn't recognize the above "problems", so you are probably just using the analogue out of the WDTV. Now anything can happen in there, and it even could be so that a 24/96 file is accepted, but first is downsampled for the DAC in there (of which I don't know what it is). But I honestly don't think I would care at using a device that needs to be controlled by the TV (which is not bad at all in this case).

 

I know, this was not much of help, but maybe you can do at least something with it.

 

Peter

 

[Audio_ELF]

No other help as to suitability, etc ... but page 5 of user manual "Product Overview"

 

Additional features

[..]

Toslink (optical) audio port

[..]

 

Whether it SRC to 48khz I don't know ... might be worth trying some of the more AV Orientated forums as this device seams more widely used in AV setups than pure Audio ones.

 

Eloise

 

[PeterSt]

Shoot, I'm sorry. I already didn't feel confident about it, but now I recall that my DAC doesn't have an optical in, so I just can't use it.

 

Ok, now I have a different answer :

 

There is no single reason why the output should not be bit perfect, unless indeed sample rate conversion takes place, which in this case is more then less likely because the device is very inexpensive, and its target will be video hence 48KHz (audio for video is always 48KHz for normal DVDs and normal HD).

 

So, the only thing you need to check (somehow) is whether 44.1 comes out if you put that in.

If it does, there is no reason that it's not bit perfect (it is not a Bill Gates thing ! :-)

 

Peter

 

 

 

[Olive Empithrie]

I bought a WDTV mainly for photo and video viewing. Listening to 16/44.1 via the optical out it is difficult to detect the difference between this and my laptop via USB. Laptop wins but only just. So if you can put up with the somewhat clunky interface --you need to navigate up and down your directory structure to select an album -- the sound is superb in value for money terms.

 

The problem, and the show stopper for now, is gapless playback is not supported. There's a gap inserted between tracks of approx 2 sec. which is not much fun when Dark Side of The Moon is playing. Hopefully WD will release a firmware fix for this.

 

[anm]

I don't have one, but looking at the pictures it seems there is an optical out.

I read somewhere that it can play from playlists. How exactly, that I am not sure of.

When you say laptop is slightly better in playback, can you please point out what the difference is?

 

regards