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High End DAC for Lossy File Playback
Horizons
post Jun 17 2008, 17:26
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I have all of my music in iTunes at AAC 256 VBR. I drive a high end system with my iPod via the line out connector. Sounds surprisingly good.

Always looking for an upgrade, does it make sense to try the Wadia iTransport and feed this to a high end DAC? What are the practical considerations of using a high end DAC when the files have already been compressed with lossy AAC?

TIA
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DVDdoug
post Jun 17 2008, 19:24
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Disclaimer - I tend to be skeptical about... everything! tongue.gif And, I don't have any personal experience with high-end DACs.

A good 16-bit DAC isn't all that hard to build*, and I doubt you'll hear any difference in DACs under "normal conditions". (By normal conditions, I mostly mean reasonable gain/volume levels and full-scale normalized audio files... If you have low-level signals and lots of gain, bit-resolution and noise come more into-play.)

If there is an improvement with the iTransport, I would assume it's mostly because you are bypassing the iPod's output-amplifier. And, you may get some improvement by simply connecting that output to an external amplifier. The external amplifier-input will have higher impedence than a pair of headphones, and this puts less load on the iPods internal amplifier (it's putting-out less current).

Of course with an iPod, the only way to bypass the output amplifer is to bypass the internal DAC too.




* Building a good ADC is much more difficult.
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Horizons
post Jun 17 2008, 20:42
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OK, so then maybe it really comes down to the quality of output stage (opamps?) vs the quality of the DAC?

Not sure which DAC and output stage type is in the latest iPod classic.
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pdq
post Jun 17 2008, 21:20
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Much harder than the 16 bit DAC is the analog lowpass filer that must follow it if theDAC operates at 44.1 kHz. Nearly all DACs these days upsample the digital data first so that the lowpass filer becomes much easier to implement.
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Roseval
post Jun 17 2008, 21:36
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As far as I know, the Wadia bypasses the entire DAC of the iPod
http://he-japu.blogspot.com/2008/01/wadia-...-ipod-dock.html

or http://www.wadia.com/support/170iTransport_faq.htm
Tip: try Google


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seditious3
post Jun 21 2008, 03:32
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I believe that using a high-end DAC (or a Wadia transport) on lossy files makes no sense. Do you have these files lossless anywhere?
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Horizons
post Jun 24 2008, 20:32
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>>Do you have these files lossless anywhere?

Yes, I have all of my files on a hard drive in Apple lossless.

>>believe that using a high-end DAC (or a Wadia transport) on lossy files makes no sense.

That is my basic question. I am wondering if a high end DAC will make AAC lossy files sound any better than through the ipod dac.
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cabbagerat
post Jun 24 2008, 20:45
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QUOTE (seditious3 @ Jun 20 2008, 18:32) *
I believe that using a high-end DAC (or a Wadia transport) on lossy files makes no sense.
Why would you believe that? The type of distortion introduced by a DAC is mostly different from the type of distortion introduced by lossy codecs. If your lossy codec is transparent, and you can ABX one DAC from another, then you want the better DAC, don't you?

QUOTE (Horizons @ Jun 24 2008, 11:32) *
That is my basic question. I am wondering if a high end DAC will make AAC lossy files sound any better than through the ipod dac.
Probably not, but that's got more to do with the environment in which you listen to your iPod than with the DACs. Even if you can (and you probably can't) ABX between the iPod DAC and a better one in a quiet environment, that doesn't mean you could do the same in a noisy one.


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dragonslayer786
post Jun 24 2008, 23:44
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This is something that interests me as well.

It didn't take long to figure out that there is a lot of misinformation on Head-Fi, but is there any truth to the need for a high quality DAC for the best playback? Some of the people there spend a 100 USD on external DACs but others spend thousands, is there any PROVEN advantage to purchasing such equipment rather than using a PC's onboard soundcard's DAC or an iPod's DAC?
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slks
post Jun 25 2008, 00:37
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Onboard sound on computer motherboards generally suck because they resample (poorly) and they are poorly designed and not isolated from the other circuitry in the computer, which leads to high, audible levels of noise. There is a definite advantage of having, say, a $120 external M-audio sound card (not really a card, but whatever) over onboard sound. But is there any appreciable difference between that M-Audio card and these ones you speak of that cost thousands of dollars? I'd wager to say no.


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dragonslayer786
post Jun 25 2008, 00:40
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Often members subjectively evaluate these cards based on the characteristics of the sound the DAC produces compared to others such as one sounding "warmer" than the other or "more revealing". Are these plausible claims?
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Horizons
post Jun 25 2008, 18:48
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Maybe a more direct and real question would be:

What is the limiting factor - DAC quality or compression quality?
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Horizons
post Jun 25 2008, 21:12
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Found an interesting post from a UK based site:

"The prevailing wisdom is that the higher the bit rate the track is encoded in the better the quality, and the uncompressed is better yet. While this is true - it remains a fact that the human ear cannot perceive these differences beyond a certain point. Once you have a AAC encoded above 160 or so it starts to become indistinguishable.

The real clincher is the DAC (Digital Audio Converter). Digital audio conversion must be done regardless of the compression format or lack thereof. It's the changing of a string of binary data into soundwaves. If you have a high end stereo system, or PC with a serious studio quality sound card and speaker setup you will hear the difference between different compressions up to about 160, but not beyond unless you have seriously trained ear.

Carrying around lossless files on an ipod is really pointless because the DAC is the weak point. It's just too small to have proper DAC. Even with top of the line earphones in a soundproof room you won't tell the difference beyond 128 on an iPod (on AAC that is, MP3 is over 20 years old and quite sucky so larger files will make a difference).

...but that said, it's nice to have the larger files on the computer with the good DAC (and the Apple PCs native soundcards' DACs are not too shabby) and not have a separate library of smaller files to sync with the iPod."
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greynol
post Jun 25 2008, 21:47
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QUOTE
It's just too small to have proper DAC. Even with top of the line earphones in a soundproof room you won't tell the difference beyond 128 on an iPod (on AAC that is, MP3 is over 20 years old and quite sucky so larger files will make a difference).

This is nonsense, as are some of the other statements which I did not bother to quote.

FWIW, I've seen it suggested that some artifacts are easier to hear with crappy pc speakers, though it seems that a decent set of headphones can help in the majority of situations.

One needs to cite results from properly conducted blind tests to determine if people can tell the difference between different DACs, otherwise this discussion is pointless, in fact it should be discouraged. Read #8 in the Terms Of Service if you have any questions.

This post has been edited by greynol: Jun 25 2008, 21:48


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dragonslayer786
post Jun 25 2008, 23:50
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Can we see a link to this site, so we can determine how believable that statement is? Claims without evidence are essentially useless.
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