What exactly does a DAC do?

rnp614

There's a Rotel RDP-980 available in my city on audiogon, and I'm thinking about getting it just to add the optical out ability to my RSP-980.

2 questions:

1) What exactly does a DAC do?

2) Does anyone have any experience with that particular unit?

rnp614

Thought I should add in that my source for most music is my computer.

VR3

Digital To Analog Convertor...

rnp614

But are there any gains in having one? How does it work? Would there be a big difference from analog out from soundcard to using optical out on soundcard?

RuSsMaN

Ask Polkthug, and Jhdiggs. They are our resident guru's on all things audio. They might even have a chart or graph to prove it.

It depends on your source. If anything, a separate DAC takes separates to the NEXT level, providing yet another separate power supply (from your laser assembly and transport), this time for Digital to Analog conversion.

I would also suggest you use an upgraded (true 75ohm if possible) cable to realize the FULL benefit, but then again, why? We all know ALL cables sound EXACTLY the same. I hear a coathanger can actually pass a digital signal, with few errors.

Cheers,
Rooster

dkg999

Russman - you are absolutely correct on the fact that all cables sound alike! I have no less than 20 different pairs of IC's and speaker cables laid out on the floor, and I have put my ear up to each pair, and I can't tell any difference in sound between any of them. I could swear that one pair of BJC IC's said "let me the f___ out of here", but that would be a subjective opinion not based in scientific fact.

RuSsMaN

Hey, if you can't put it on a pie chart and prove it, I'm not talking to you anymore. You are full of fecal matter on this one.

Cheers,
Rooster

dkg999

Now you have went and told everyone about the "rubbing your cables in fecal matter" tweak that makes a piece of Home Depot 16g lamp cord sound like a $1000 AudioQuest speaker cable. I thought we were clear that this secret would just be between us? It's a no love thing here tonight!

PolkThug

Originally posted by RuSsMaN
Ask Polkthug, and Jhdiggs. They are our resident guru's on all things audio.

Cool! I've made it a long way in a year and a half, but I think you're giving me too much credit.

Regards,
PT

Kevinvb11

Just a quick input on cable matter.

When a CD player reads a cd, it reads 0's and 1's. For example:

player one reads: 00101010011001010.

player two reads: 00101010011001010.


Now take that into consideration with a reader or transport. When you have a dedicated DAC, or any DAC for that matter, it wlll influence that information as it forms it into an analog signal. But, that signal it gets from point A to point B is still the same regardless of source. Point A to B being the signal from CD Player to DAC.

When a CD player sends its' signal to the DAC it is the same regardless of an on board DAC or off board. Why???, because it reads the same 0's and 1's that any other player would.

All the sound differences form one player to another come from the DAC. This is what makes a good player sound good and a good player sound bad. The cable in between makes no difference.

Now take that theory and apply it to all your point A to B sources/processors. Whether it be a CD player, DVD player, video converter, DAC etc etc, it's still a cable just passing along the info.

If you change out a $3K coax cable with a radio shack $2.99 special, you will hear no difference between you CD player and DAC. Why, you may ask? Because that $3k cable still passes along the same 0's and 1's that the $2.99 cable did. But, change the DAC from one to another and you hear night and day difference depending on your likes. Because that is processing and that DOES make adifference.

When it comes to source cables, if you do hear a difference it's probably a voice, very close to the back of your head, telling you to justify the purchase and "listen" to a difference in something. And why??? Because nobody want to spends hundreds and thousands of dollars without hearing a difference.... So they "hear" one, and that's all it takes to justify the cost of cable.

Kevin



Looks nice, doesn't it?

danger boy

A DAC will make any digital signal sound better. it's similar to the difference between a recevier. and seperates. the seperates in most cases is going to sound quite a bit bettttter.

2+2

Kevin, as to the little voice re cables...sorry but you are simply wrong....I have preferred cheaper cables over more expensive ones...just like I have preferred 65 watts of HK receiver power to 120 watts of Rotel amp power.

I have also recently been forced to admit that in view of playing with 2 different cd players hooked up digitally to pass just 1s and 0s to the DACs in the receiver, they sound different, eventhough they use the same DACs. I actually had your view...that all 1s and 0s are created equal. The reality tells me different. My engineering background doesnt quite understand why but the difference is there....but I learned long ago of limitations in science.....

edit....that is not to say that the little voice factor does not occur with others....obviously, I am speaking for myself...

jdhdiggs

Originally posted by PolkThug
Cool! I've made it a long way in a year and a half, but I think you're giving me too much credit.

Regards,
PT

Exactly what I was thinking. Did you get you "Audiophile Guru" card in the mail yet, I'll be getting mine on Monday!

To the original question, the external DAC just replaces the DAC in your CDP or the one in your reciever/processer.

As Sid said, its a digital to analog converter. Somewhere in your chain you need to do this. If you use a digital in on your processor, you're using the one in there, if you analog out of the CDP, your using the CD's this just adds another otion in the chain.

In my mind, the external DAC give you an oppurtunity to tweak and change what you hear without making wholesale changes in your gear. Lots of interesting reading on various chipsets out there. Play around with it. It won't hurt anything but your pocketbook.

Also, same DACs will sound different given the programming gone into them Different end customers can order the same part, but then program some of the output charectorsitics. Similar to you and I owning the same computer. If I run Linux and you run windows, there will be differences even thought the chip is the same. The outputs on the analog side can also make a difference.

Kevinvb11

Concerning the opoinion that CD/transports sound different, would it be because certain players read the information more acurately, or is there a break down and loss of the information somewhere between the actuall CD and the coaxjack/digital out?

I only ask because the information on a CD is the same for all players. A certain cd doesn't say I'll play all the information for this guy and I'll leave a little bit out for the other...

Maybe I missing something here, but don't you guys think all quality players/transports should sound the same? I mean they can only read alll the information and then pass it on to the DAC where then it will sound different?

Emlyn

Originally posted by Kevinvb11
... but don't you guys think all quality players/transports should sound the same?

No, you're missing something.

Kevinvb11

I guess I should have said that if a the player is strictly a transport to send information to a DAC, then it should read the information of the disc unchanged and in it's original form. I'd want a transport to grab that information and get all of it without any colorizing or transforming the information to make it sound diferent than what the original artist intended.

After that you can find a DAC to your likes and let that handle the representing from there on out.

Does this make sense??? Or does it just not work like that at all?

RuSsMaN

Jitter is a big issue with different transports. As is the quality of the laser assembly and the motor. A lot of CDP's with 'coax' dig output don't use a true 75ohm jack, most are standard 20-25ohm RCA.

There are a lot of variables that come into play.

Oh, and it's RARELY as the 'artist' intended - it's how the the guy in the booth pushing sliders intended.

Cheers,
Russ

Kevinvb11

Originally posted by RuSsMaN
Jitter is a big issue with different transports. As is the quality of the laser assembly and the motor. A lot of CDP's with 'coax' dig output don't use a true 75ohm jack, most are standard 20-25ohm RCA.

I see. Yes there are many variables.

Oh, and it's RARELY as the 'artist' intended - it's how the the guy in the booth pushing sliders intended.

I agree, it's the producer mixing everything down. But I do know of quite a few artist who have the say when it comes to the mix down. Or, with some of the bands that I listen to, do there own mixing.

LuSh

To suggest a digital cable can't make a difference from point A (transport) to point B (DAC) is a sure sign of inexperience. Will it make a difference in all cases? No. But the higher you move up in the chain the larger those differences will become. I have compared a $400 Moray James cable to a $400 Harmonic Tech Cyberlink cable and the differences were so striking that I was accused of changing something other then the wire, perhaps the amp, to a non audiophile friend. I've never tried but I doubt you'd have such a startling result when connecting a $100 DVD player to an HK receiver because you're not at a crucial point where it will make a difference. The overall system resolution isn't high enough to chart or notice these differences, but if you have a very high resolution system then yes, small changes like a digital connection will pay huge dividends.

In my own experience Transports have made less of an impact but I haven't tried too many in my own system. Some swear that it will make a bigger difference then the DAC and cable because without getting every last 1 and 0 the DAC isn't receiving the most accurate information in which to process.