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In my long and arduous journey towards understanding the ins and outs of hi-fi audio I have hit a road block. What is the difference between a DAC and a decoder? When reading reviews for Blu-ray players or AV receivers I often hear them talk about how they can decode Dolby True HD or DTS-HD Master Audio, does this mean they automatically have a good DAC as well?

It is likely that they have a DAC if they have analog outputs but how good that DAC is cannot be presumed.

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One would think that a device with the ability to decode the highest quality audio formats, would also come equipped with a very good DAC.

Not necessarily. The decoding function is all digital and defined by the license for the particular HD format. OTOH, the DAC can be implemented well or poorly and the resulting signal quality is dependent on the design of the analog stages as well.

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Although I think I have a broad understanding of these two functions, I'm still a little fuzzy on exactly what they each do, and what the differences between them are. While I know to look for players and receivers that can decode Dolby True HD or DTS-HD Master Audio, how do I know whether my player or AV receiver comes equipped with a good DAC?

As with most things in audio: Reputation of the manufacturer, specifications, reliable reviews and, of course, listening.

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Also, where in the audio signal chain do you recommend having the digital to analog conversion done?

Opinions vary but I offered a relatively full discussion of this in the latest MITR: http://www.stereophile.com/musicintheround/music_in_the_round_44/

Kal

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When reading reviews for Blu-ray players or AV receivers I often hear them talk about how they can decode Dolby True HD or DTS-HD Master Audio ...

What you are mentioning are audio formats. The processor can decode (or convert) an incoming data stream to a specific format of out going signals which are then sent to the amplifier/speaker with the appropriate levels, delays and effects, etc. The final product is then labelled DTS-HD or Dolby True HD or even, going back in time, Dolby Pro Logic Surround. Each format has a distinct sound but the nuances of sound quality and the satisfaction you derive from a specific product can vary between processing chip manufacturer and processor design. A Marantz and a Harman Kardon would very likely sound unlike one another when you listened carefully and neither would probably compare note for note and thermo-nuclear implosion to thermo-nuclear implosion to, say, an Outlaw. As Kal has suggested, there is more to a component's overall performance and quality than a single chip would explain.

Therefore, the ability to decode the latest playback format indicates the most contemporary design but not automatically the highest quality chip or processor design. A $400 HT receiver might decode the same formats as a $4,000 stand alone processor but it would be highly unlikely the two components would have more than that in common.

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... does this mean they automatically have a good DAC as well?

I hope the above has answered that question. The answer is, the ability to decode a format in no way speaks to the quality of the product or its component parts.

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Also, where in the audio signal chain do you recommend having the digital to analog conversion done?

Since nothing in the way of lost information or sound quality can be put back into the signal further down the chain and losses will only be exacerbated with more processing, I would tend to place the conversion process as early in the signal chain as possible.

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What is the difference between a DAC and a decoder?

The decoder function decompresses and unpackages a digital content stream which has been encoded via a particular format (e.g. FLAC, DTS-HD) and outputs a PCM stream. This stream may be further processed by room correction or other processing and is eventually delivered to the DAC for coversion to analog. The encoder and decoder functions are often referred to as "codecs".

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When reading reviews for Blu-ray players or AV receivers I often hear them talk about how they can decode Dolby True HD or DTS-HD Master Audio, does this mean they automatically have a good DAC as well?

As described in other responses in this thread, the presence of particular codecs has no bearing on the quality of the DACs.

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how do I know whether my player or AV receiver comes equipped with a good DAC?

As Kal described, by the vendor's reputation, reviews, specs and listening.

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Also, where in the audio signal chain do you recommend having the digital to analog conversion done?

My thought is that the conversion to analog should happen only once and as close to the amp as possible. Many A/V receivers convert any incoming analog to digital for further processing prior to reconversion back to analog. My recommendation would be to use the best possible receiver/processor and feed clean digital to its inputs. In this model, there is no need to have expensive DACs and analog processing in the player.

From your description, can I assume you cannot connect HDMI directly to your receiver?

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Right now I have my DVD player connected to my TV via HDMI cable. I them have the tv connected to a receiver via toslink. Is there any loss of information in the tv between the HDMI input and toslink output?

Yes if you receiver can accept HD audio and/or multichannel via HDMI. Toslink from the TV will not carry that.

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Would you recommend that I use the toslink output from my DVD player to connect it directly to the receiver, or am I fine just connecting it with HDMI to the tv and then connecting the TV to the receiver via toslink?

I would suggest you try the direct Toslink-receiver and see if it makes a difference.

Kal

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So only HDMI can carry HD Audio?

HDMI can carry multichannel hi-rez audio data; Toslink is limited two 2 channels, and then only up to 96kHz sample rate. (Some components can transmit and receive audio at 192kHz sample rate via Toslink, but it is dependent on the quality of the Toslink cable.)

John Atkinson
Editor, Stereophile

It's been a few years since I started this post, and my system, as well as knowledge, has made a number of upgrades. I currently have a Samsung BD-C6500 Blu-ray player connected via toslink to a Music Fidelity V-DAC I. That is connected via RCA cables to a Denon AVR-2807 receiver. 

Anyway, since the V-DAC only has stereo output, I'm assuming that if it receives a 5.1 or 7.1 signal it converts it down to stereo. That's all well and good for most music, but when watching blu-rays or listening to any multi-channel sources, I'm assuming it's bad for the signal to be downconverted to stereo in the DAC, and then upconverted in the receiver. I'm also assuming that the V-DAC is a better DAC than the one in the Denon Reciever, but with all this up and down converting going on, is it worth it to still send the signal to the V-DAC when watching Blu-rays or should I connect the Blu-ray player directly into the receiver?

Also, Merry Christmas!

Tomdabomb09 wrote:

since the V-DAC only has stereo output, I'm assuming that if it receives a 5.1 or 7.1 signal it converts it down to stereo.

Thta's not correct, I am afraid. When a 2-channel DAC receives an S/PDIF datastream with encoded multichannel audio (Dolby Digital or DTS) , it will mute its output. If you are hearing audio from the Musical Fidelity V-DAC, this suggests the Blu-ray player is just sending it the front left and right channels packed into the S/PDIF stream.

Tomdabomb09 wrote:

Also, Merry Christmas!

And to you.

John Atkinson

Editor, Stereophile

Do you think it would be better to have my blu ray player output 2 channel audio to the V-DAC or have it send the full multichannel audio directly to the receiver?

I am hearing impaired and recently purchased a stethoscope hearing device for watching movies streamed on my TV. Because my Samsung TV only had a digital/optical audio output and my stethoscope hearing device needed RCA inputs, I purchased a Gefen DCA to RCA converter (GTV-DIGAUD-2-AAUD). With the Gefen converter installed, my stethoscope device produced good sound for cable TV; however when trying to watch streaming movies all I heard was a continuous clicking sound. According to Gefen tech support, I should use a DCA decoder (GTV-DD-2-AA). I'm confused can you please explain why the Gefen DCA converter worked for cable TV programming but not for streaming movies.

The GTV-DIGAUD-2-AAUD converts stereo PCM audio to analog stereo.
The GTV-DD-2-AA will do that but it also converts "up to 5.1-channel audio encoded in Dolby Digital Surround to L/R analog audio."
Apparently, the movie audio is DD encoded (typical). So, you can either buy the new decoder or see if there is a way to tell the Samsung to convert the DD to PCM so that you can keep using what you have. Some TVs will offer that option and some will not.