how does an external DAC work with a cd player?

[mibson]

On high end audio systems when there is a cd player conected via digital cable to an external DAC, does the cd player use its DAC at all? or is the information on the cd (wave) sent to the external DAC digitally in wave format? OR does the cd player convert the wave file to PCM and then the external DAC converts the pcm to analog?

 

[TLS Guy]

On high end audio systems when there is a cd player conected via digital cable to an external DAC, does the cd player use its DAC at all? or is the information on the cd (wave) sent to the external DAC digitally in wave format? OR does the cd player convert the wave file to PCM and then the external DAC converts the pcm to analog?

Only the transport of the CD player is used not the DACs

 

[MDS]

or is the information on the cd (wave) sent to the external DAC digitally in wave format? OR does the cd player convert the wave file to PCM and then the external DAC converts the pcm to analog?

WAV is a PC audio format. It's basically a header with information like sample rate, bit depth, number of channels, etc followed by the actual PCM samples. The audio on the CD is PCM and only becomes WAV when you rip it and create a file to save on your hard disk.

When the CD player is connected digitally to an external DAC, the player is simply reading the PCM from the disc and sending it to the DAC. The DAC will then convert it to analog.

 

[finite9]

sorry to re-awaken an old thread, but I have a follow on question to this post...

I understand that a CD player will just transport the pure PCM signal from the CD to the external DAC, but what if I have a media player (in my case an Apple TV2) that is playing FLAC files from my server? At the moment, I connect my Apple TV to a receiver via HDMI, which _is_ digital, but I am under the assumption that the Apple TV is decoding the FLAC file to PCM, _and_ sending it through it's own DAC before sending the processed signal through the HDMI to the receiver.

If I connect an external DAC using the Apple TV's optical out, will the Apple TV _still_ decode the FLAC file, _and_ process it through it's own DAC before sending it through the optical out connector to the DAC?

Secondly, forget for a minute that I listed a specific device... do 'players' in general decode non-PCM formats and then process them using their own DAC, irrespective of whether i've connected an external DAC or not? Or does the fact that i'm using optical out instruct the player that it shouldn't use it's own DAC?

I have 2 disc players; a Pioneer DV-656a and a Sony BDP-3500 or something... can't remember exactly at the mo. My Pioneer plays SACD using it's own DAC and analogue cables to my Denon 2310 receiver. It sounds fantastic. I play the same disc through the Bluray player over HDMI to the receiver and it sounds a lot inferior. My receiver has a DAC that is equivalent to my Pioneer, so I suspect that my Sony BluRay player is using it's own DAC (it's a really cheap player) and that is the reason for it sounding so naff. I am correct in my assumptions?

 

[jonnythan]

A DAC is a digital analog converter. The AppleTV is not going to convert from digital to analog internally just to convert it back to digital to send it over HDMI.

In the case of the disc players, you're probably using a different sound mode or setting on the receiver for the two different inputs.

 

[Grador]

My receiver has a DAC that is equivalent to my Pioneer, so I suspect that my Sony BluRay player is using it's own DAC (it's a really cheap player) and that is the reason for it sounding so naff. I am correct in my assumptions?

In addition to what jonnythan said, which is all correct, I'd like to comment on your SACD statement. Unlike CDs which are PCM, SACDs store the sound information in a different format called DSD. My understanding is that this requires the use of a different DAC than the one used by all the other inputs [which are PCM]. I would venture to bet that jonnythan's comment about settings is probably correct though.

 

[Grador]

I also think you may be confusing a DAC with decoding. When playing FLAC files on your appleTV, the player is decoding the FLAC file into PCM, which is sent over HDMI or optical to the receiver which uses a DAC to take PCM [which is simply a mathematical representation of the sound waves] and make it into an analog signal.

 

[vinicior]

Hi

As much as I remember, as I had read about this mechanism in my college days that cd player uses PCM to send digital signals i.e. PCM output goes to DAC and then we get the desired output.

 

[finite9]

thanks for the comments. I _am_ confused about it all, which is why I blabbed on so much, but can I just ask another question following on from Jonnythans comment...

Apple TV decodes input stream to PCM then sends over HDMI cable digitally to the other end... which could be a basic TV. Does that mean that TV's all have their own DAC? I'm not being funny, I just didn't realise that this was the case. I thought DACs were always in the player or reciever. I think I already know what you're going to answer, so sorry in advance for it being a stupid question. Suppose I never thought about this hard enough before posting

I connected my Apple TV using an optical cable instead to my receiver, but there are no options in ATV to choose the output, and HDMI always needs to be connected , so I have absolutely no idea if it's sending sound through hdmi or optical, and I suppose after reading the comments that it'll make no difference whatsoever?

What I was really trying to get at was if it was worth buying an external DAC like a DacMagic, because if a digital signal is going straight to my receiver DAC anyway, then I don't see the need.

I suppose the answer to all my original questions is that if I use an analogue cable then the player always uses it's own DAC, even if it's sending the signal to a receiver with it's own DAC, but if I use _any_ sort of digital cable like HDMI or optical or sp/dif then it sends out a digital signal to "the other end" and bypasses it's own DAC entirely?

 

[jonnythan]

Anything that can take a digital input and output an analog one (whether through speakers or an analog output) has a DAC. A DAC is literally just a chip that converts a digital input to an analog one.

Every TV that has any sort of digital input (including an antenna input for digital TV) has one.

There is generally no need whatsoever to buy an external DAC, ever. Your money is much better spent elsewhere (like speakers).

Look at your system hookup and determine which product is converting to analog. That's the DAC you're using for that source. CD player's analog outputs? CD player's DAC. CD player digital output to receiver? Receiver's DAC. Etc.

 

[ldgibson76]

Anything that can take a digital input and output an analog one (whether through speakers or an analog output) has a DAC. A DAC is literally just a chip that converts a digital input to an analog one.

Every TV that has any sort of digital input (including an antenna input for digital TV) has one.

There is generally no need whatsoever to buy an external DAC, ever. Your money is much better spent elsewhere (like speakers).

Look at your system hookup and determine which product is converting to analog. That's the DAC you're using for that source. CD player's analog outputs? CD player's DAC. CD player digital output to receiver? Receiver's DAC. Etc.

I do agree that speakers can have the greatest impact on sound quality.

But, the above statement regarding the DAC's....... that opinion is subjective at best! It's all relative. A high quality DAC can definitely produce a better conversion yielding better overall sound quality when compared to the DAC's that are equipped in a AVR or CD Player or a music server. Are there AVR's and CD player's with high quality DAC's? Of course. But it comes at a cost. They are usually much more expensive. With that scenario, you are definitely closing the gap, but more times than not, adding an external DAC will produce better SQ. There are many DAC's (internal and outboard designs) with various levels of performance. Contrary to popular belief, all DAC's are not the same. Implementations are different from device to device.
The S/N ratio, dynamic range, and THD measurements are barometers of the quality of the DAC along with implementation.

I know for a fact that the external DAC I've integrated into my system produces a marked improvement in sound quality when compared to when my AV Processor, Apple TV or my HTPC are doing the conversion.


Here's my advice, purchase a external DAC. Make sure the retailer has a decent return policy. Integrate it into your system then compare. If you hear an improvement then keep it. If not return it and continue to rely on the
source devices for the conversion.

 

[jonnythan]

Before you take ldgibson's advice, be aware that he's using about $2500 worth of amplifier connected to a $1500 pre-pro.

Anyway, I challenge ldgibson to post the S/N ratio, dynamic range, and THD measurements of a midrange Denon or Onkyo receiver's DAC and compare them to a typical external DAC.

 

[finite9]

ok well im happy with the answer. It confirms my hopes that the Apple TV is not doing the conversion, but my receiver, which is what I wanted. When xbmc releases their next stable release with rewritten HD audio engine, it will be sending out my 24bit FLACs in their true 24/96 state as 24/96 PCM straight to my receivers DAC I didn't want my Apple TV hardware getting in the way of this.

I don't know what kind of quality my receiver DAC has, but it was a midrange receiver so im hoping its ok when compared to a dedicated external DAC. It might not be upconverting to 24/192, but is that alone going to make it sound great when the input is only 16/44 FLAC?

I still wonder why my Pioneer DV656a sounds so good though compared to my receivers DAC. I thought they were equivalent. Connected the Pioneer using Argon cables on 2ch. Playing SACD DSD stream on 2ch section only to receiver.

I know it's not a like for like comparison, but I ripped the CD section of the SACD to my server as FLAC (figuring that the mixing of the master had more bearing on the SQ than the fact it was SACD vs CD format), and played it back through my Apple TV to receiver. I also played the SACD as DSD 2ch from my Sony DBP player using HDMI to receiver, and that it where I notice the biggest quality drop (larger than with the Apple TV). My Denon AVR-2310 receiver has the same settings in the menus for all channel inputs.

So im playing the same 2ch DSD disc section on both players, but one uses its own DAC, the other uses the receivers DAC. Is it just the DAC that is affecting the sound quality in this case or is it the whole hardware component package (pickup, transport etc) of the Pioneer vs the Sony that affects the output?

 

[Grador]

ok well im happy with the answer. It confirms my hopes that the Apple TV is not doing the conversion, but my receiver, which is what I wanted. When xbmc releases their next stable release with rewritten HD audio engine, it will be sending out my 24bit FLACs in their true 24/96 state as 24/96 PCM straight to my receivers DAC I didn't want my Apple TV hardware getting in the way of this.

I'm pretty sure you can play back 24 bit FLACs right now in XBMC, the HD audio rewrite will add support for bluray HD audio codecs.

I don't know what kind of quality my receiver DAC has, but it was a midrange receiver so im hoping its ok when compared to a dedicated external DAC. It might not be upconverting to 24/192, but is that alone going to make it sound great when the input is only 16/44 FLAC?

Upconversion is not only unnecessary, but undesirable. You do not add any information when upconverting as there is only the information given to work with, but you can add noise and other errors into the waveform during the process of making up the extra numbers to add to the stream.


If you'd like or need I can give you a little more detail on PCM and how it works, just ask.