# To DAC or not to DAC, that is the question.



## Guest (Apr 11, 2007)

What makes a DAC (Digital to Analog Converter) good or bad? I have always found that digital source material sounds better when it is left digital for as long as possible. Hence I always leave everything digital and let the recievers DAC handle the data. Why would an outboard DAC be better?


----------



## Otto (May 18, 2006)

Hi Nick,

I can try to start this out. I once knew a lot about signal processing, but it's been a while. 

Like any engineering application, there are lots of considerations put into the design of a DAC. Basically, it's the way in which all the digital data is recombined into an analog signal, and the methods of doing that are varied.

First, there are basics that go into it. Is the power supply good? Some are better than others. Is the unit itself properly designed to reject noise and other junk? What's being used for analog processing? I used to have a tube-based DAC that offered a different sound because of its analog processing (the tube). 

Digital signals can "alias" up into higher frequencies based around the sampling rate. Therefore, they do processing to effectively increase the sampling rate. This is called oversampling, and I've heard people mistakenly think that this is related to the number of times the device reads the track on the disc. It has nothing to do with the reading of the data, but rather with the reconstruction of the data into an analog signal. To get cut this aliasing out, an analog filter is used. Because there is no brick-wall filter in real life, they oversample the data so that it aliases at a much higher frequency than normal (I'm a little foggy on where aliasing exactly occurs -- at the sample rate, double the sample rate), and then employ the analog filter to the signal such that we don't get any other aliased audio components in there. So, the oversampling and analog filters that are used play a part.

Increasing the word size is another technique where the "normal" 16 bits of audio data is "interpolated" into a higher resolution format -- for example 24 bits. If done well, this may yield an improvement in sound, as there should be greater resolution with which to work. This may be referred to as upsampling.

Increasing the sampling rate is another method that's used to play with the data. Normal CD is sampled at 44.1 kHz, but you may see machines process things like 24/96, where those indicate 24 bits and 96 kHz, respectively. The more frequently you sample data, the more close it is to the original.

So, there's a start. I'm being a little loose on my descriptions, mostly because I don't deal with this stuff much anymore. I'm sure there are others around here that can correct my mistakes and fill in the blanks!


----------



## jackfish (Dec 27, 2006)

In the realm of home theater, digital-to-analog conversion is often left to either the source transport (DVD player) or the receiver. It really depends on the transport and receiver as to which DAC is going to perform the best. So, it is not true that it is always best to keep the signal digital as long as possible. If your transport has a better DAC than your receiver then it would most likely make sense to let the transport do the conversion. Most component DACs are stereo only (I've never seen a 5.1 or 7.1 DAC, perhaps they're out there), requiring a downmix to stereo (usually S/PDIF to PCM) to be performed by the source transport.


----------



## Otto (May 18, 2006)

So, who out there is using a good 2-ch outboard DAC?

I'm starting to consider going back to an external DAC for stereo processing. Any suggestions?


----------



## jackfish (Dec 27, 2006)

Benchmark DAC1 always gets mentioned as one of the best.


----------



## Otto (May 18, 2006)

Yep, my boss has the Benchmark. He's going to be bringing it over, perhaps today, to do some listening. I'll let you know my impressions on any differences from what I'm using now (the DACs in the Outlaw 990).


----------



## Guest (Apr 15, 2007)

Otto said:


> So, who out there is using a good 2-ch outboard DAC?
> I'm starting to consider going back to an external DAC for stereo processing. Any suggestions?


Channel Islands Audio has their VDA-2 with outboard PS VAC-1 (external PS highly recommended). Dusty and his company is great to deal with, and they also have a 30 day return if you do not like it.

Dan


----------

