2. digital
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mp3 bit stream to DAC?

I have an mp3 player (archos av340) which in addition to the headphone analogue audio out, has an SPDIF out. I used to plug the SPDIF out to my yamaha tuner/reciever/amp SPDIF in and play through my stereo system. The SPDIF out/in gave much better sound than the archos analogue out/ yamaha analogue right/left in's I used before I learned I could go the "digital" route (I guess the yamaha had a better DAC than the archos?).

The question - I bought new speakers (quad 989's), a tube amp and an ACK DAC 2.0 to be able to again play my mp3's the digital route through my new system. I get NO sound or indicator light "on" on the ACK indicating the ACK is getting a digital signal fed to it. Should the ACK (or any other DAC for that matter) be able to get and DAC mp3 bit streams (like my yamaha reciever did)? If so, any thoughts on what I could be doing wrong.

Finally, I know mp3's through a "nice" system is an oxymoron (i.e. the mp3 signal is compressed compared to a raw CD signal), but, most of my music is mp3's so I still want to make things work.

????
hovendic
steuspeed's avatar
steuspeed
501 posts
 
Hovendic,

I looked around for an answer to your question, but I could not find anything specific as to what requirements a DAC needs to play an MP3. MP3 players have decoders built in them, but outboard decoders or DACs seem to be lacking. Perhaps MP3 decoding is built into more modern DAC chip sets? Your Yamaha must have this capability. If a component says, "It can play MP3" that is a bit ambigious as this can mean before or after it has been decoded to analog.

What DAC did you buy? Was there any improvement?
edesilva
768 posts
 
GCE.

The bitstream created by an mp3 is format identical (although not content identical) to a CD transport; the player has a digital algorithm in it to convert mp3s to a PCM stream that is probably 16 bit 44.1 kHz, maybe 16 bit 48 kHz (used by a lot of computers). The Ack DAC might not like 48 kHz sample rates, so that might be it. Most DACs are more tolerant.

The content difference is that your mp3 is going to sound compressed, even though the stream is no different technically. It still has to create the same sample rate and reconstruct the bits, its just that it has less information to do it with and will therefore interpolate a lot more.

Try running wav files off your Archos. Those will probably sound a lot better.
hovendic OP
9 posts
 
Steuspeed - I forget the name, but there WAS a difference, in that they did play through the spdif/digital out into the new DAC

Edesilva - thanks for the input, I think you're post is exactly right. It is a PCM stream in 16 bit, 44.1 KHz, identical to any other "transport", but compressed as you say. They play "allright" to my ear but will download some wav files of some of the same songs and try to listen to a difference.

As a side note, the archos is great, but I think I am going to also get an xbox that has a digital (optical) out, store and plays my mp3's that way as well (I think I have to install some software on it first to do so though).
Still looking into it on the internet.
edesilva
768 posts
 
Are you thinking new XBox? The 360 will act as a media server and even allow access to music files on other networked computers on your LAN, as long as they are running Windows OS (actually, might have to be running Windows Media Center Edition... can't recollect). Supposed to actually be a decent UI.

The wav files will sound a lot better.
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