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A question about DACs.

post #1 of 4
Thread Starter 
I have been looking to upgrade my system and move to an external DAC, and while there doesn't seem to be anything that meets my needs exactly (ideally I would have a DAC that accepts an HDMI input, and/or has a built in audio delay option) from reading up on things, it seems like DACs are actually a "solved problem" now?

  • There are 32-bit DACs with 135dB of dynamic range that allows for volume adjustments to be made in the digital domain for perfect channel matching without introducing audible noise - analogue control will introduce channel imbalances, and raise the noise floor - at least to a point. If you have the digital volume control really low, you could potentially be down below 16-bit - but that's why many DACs have an adjustable output gain. (a fixed analogue setting that will not introduce channel imbalances, but help keep the SNR high)

  • The problems of variable noise with sigma-delta modulation have been solved with ESS Tech's HyperStream Modulator. (and presumably other manufacturers have equivalents?)

  • Modern DAC designs are completely jitter immune on all interfaces, and you can build a DAC that is ruler-flat from 0.1Hz to well above 20kHz.


If the limit of human hearing is 20kHz - say 21kHz for outliers, and below 18kHz for most adults.
And listening to anything over 90dB for extended periods of time will cause permanent hearing damage.

Where do we go from here?

As long as it is built correctly, surely anything using a Sabre DAC chip (or equivalent) is essentially perfect reproduction of the original signal?


Going to 64-bit or upsampling to higher frequencies won't matter, because we are already beyond the limits of human hearing - to sample 20kHz perfectly, you only need 40kHz, so 44.1kHz is plenty, and even 16-bit audio has a dynamic range of 96dB. (more if you use noise shaping)


Am I missing something here? Surely if the chips are properly implemented, all DACs should sound the same at this point (assuming they use equivalent technologies) and all you are paying for is connectivity, looks, and other features? (such as having a nice 0-ohm headphone amplifier)
Edited by StudioSound - 2/21/13 at 8:29am
post #2 of 4

 

Quote:

Originally Posted by StudioSound View Post

I have been looking to upgrade my system and move to an external DAC, and while there doesn't seem to be anything that meets my needs exactly (ideally I would have a DAC that accepts an HDMI input, and/or has a built in audio delay option)

 

That's not a "DAC" in 2ch audio terms; what you are looking for is basically a home theater processor (not strictly the receiver, since I assume you'd also need analog line level outputs), mostly because of the HDMI and audio delay. HDMI was originally intended for video transmission, with 1.3 getting the digital audio transmission; and AFAIK you only need the audio delay for video and multichannel to sync audio to the video, but AFAIK the adjustments on most entry-level receivers now if they even have one aren't as wide as before since HDMI1.3 ensures that both digital audio and video go from one source into the same receiver/processor.

 

However given what you're looking for in sound characteristics - you're not looking for such things as "smooth Wolfson sound" or "warm tubes" from your source/DAC - don't hesitate to get a multichannel processor. They will be more expensive though, but of course there's a more cost-efficient brand for those. Look up Emotiva, their processors (and all other equipment) retail for a lot less than, for example, Rotel.

 

Quote:
Originally Posted by StudioSound View Post

  • There are 32-bit DACs with 135dB of dynamic range that allows for volume adjustments to be made in the digital domain for perfect channel matching without introducing audible noise - analogue control will introduce channel imbalances, and raise the noise floor - at least to a point. If you have the digital volume control really low, you could potentially be down below 16-bit - but that's why many DACs have an adjustable output gain. (a fixed analogue setting that will not introduce channel imbalances, but help keep the SNR high)
     

 

While those problems of going below 16bits are a problem with implementing the gain adjustments in the digital domain, there is another way around the inherent weaknesses of analog potentiometers - a digital potentiometer. This does not implement the volume adjustments on a digital signal, but are pots with a digital control that don't have channel imbalances and don't introduce noise into the system.

 

Many DACs and amplifiers use this now for those reasons. Meier Audio also has a different implementation of this - instead of using down-up volume control buttons or the same kind of rotary control on most A/V receivers, they add an analog knob, but instead of an analog pot it's hooked up (as I understand it anyway) to an A-D converter, and every degree of movement the pot does is converted into a command to the digital potentiometer. It's basically a knob in place of the up-down buttons, so you can make quick adjustments without holding down the buttons and of course it's great for those who are used to knobs.

 

 

Quote:
Originally Posted by StudioSound View Post

  • Modern DAC designs are completely jitter immune on all interfaces, and you can build a DAC that is ruler-flat from 0.1Hz to well above 20kHz.

 

This is the DAC chip; what happens to the analog signal until it leaves that chip, particularly the analog output section, might still introduce noise and coloration. And then there's the rest of the system until it hits your eardrums.

 

Quote:
Originally Posted by StudioSound View Post

If the limit of human hearing is 20kHz - say 21kHz for outliers, and below 18kHz for most adults.
And listening to anything over 90dB for extended periods of time will cause permanent hearing damage.

Where do we go from here?

As long as it is built correctly, surely anything using a Sabre DAC chip (or equivalent) is essentially perfect reproduction of the original signal?


Going to 64-bit or upsampling to higher frequencies won't matter, because we are already beyond the limits of human hearing - to sample 20kHz perfectly, you only need 40kHz, so 44.1kHz is plenty, and even 16-bit audio has a dynamic range of 96dB. (more if you use noise shaping)


Am I missing something here? Surely if the chips are properly implemented, all DACs should sound the same at this point (assuming they use equivalent technologies) and all you are paying for is connectivity, looks, and other features? (such as having a nice 0-ohm headphone amplifier)

 

Gong back to what I said about what happens after the chip, even if the DAC chip itself is properly implemented from digital input up to the chip, analog output designs vary. In one manufacturer alone you can get several in the same product - look at how an AudioGD DAC(+HPamp) can have Sun, Moon and Earth HDAM (which essentially are still opamp) outputs so that buyers can get the flavor they want. If I'm not mistaken those refer to bright (Sun), dark (Moon) and balanced (Earth) sound.

 

So basically the market - that is, the preferences of people buying all the gear - are an important factor. What's more, what ultimately is "flat" isn't just because listeners want something colored. What a microphone can measure in a speaker or headphone, or the entire system through these, ultimately can still be a problem if eardrums don't have as flat a response as a microphone - it may have dips in the bass, or the -3db point may seem too high; or it can have peaks in the treble; etc. Even if there's nothing wrong with your eardrums human hearing is biased to some frequencies, which is why for example some people will hate the Sun opamps, chalk slipping on the blackboard (or aotherwise any scraping on it), then seek out the "smooth Wolfson."


Edited by ProtegeManiac - 2/21/13 at 7:16pm
post #3 of 4
Thread Starter 
Quote:
Originally Posted by ProtegeManiac View Post

That's not a "DAC" in 2ch audio terms; what you are looking for is basically a home theater processor (not strictly the receiver, since I assume you'd also need analog line level outputs), mostly because of the HDMI and audio delay. HDMI was originally intended for video transmission, with 1.3 getting the digital audio transmission; and AFAIK you only need the audio delay for video and multichannel to sync audio to the video, but AFAIK the adjustments on most entry-level receivers now if they even have one aren't as wide as before since HDMI1.3 ensures that both digital audio and video go from one source into the same receiver/processor.
Well I am wanting to use an external DAC for my PC. The problem is that without some kind of delay option in the DAC, audio will be out of sync. That's fine for music, but not video. I'm not looking for a HT Receiver because they are huge boxes with crap headphone outputs, and all I'm looking to drive is a pair of headphones, not speakers.

HDMI would be really convenient because the current spec transmits audio sync data, and would save me running any extra cables.

I was actually thinking along the lines of the Benchmark DAC2, because it seems to be essentially a perfect implementation of the Sabre DAC, at which point it seems like you would never have to upgrade again if it measures perfectly flat? (at least within the range of human hearing)

But if I am only using the PC as a source, it seems like the O2+ODAC might be all I need - though the analogue output is not quite as good, and I don't see any way of delaying that - there are toslink/coax delay boxes available, and toslink from a soundcard would allow me to take advantage of headphone virtual surround options when gaming.
Quote:
Originally Posted by ProtegeManiac View Post

While those problems of going below 16bits are a problem with implementing the gain adjustments in the digital domain, there is another way around the inherent weaknesses of analog potentiometers - a digital potentiometer. This does not implement the volume adjustments on a digital signal, but are pots with a digital control that don't have channel imbalances and don't introduce noise into the system.
Seems like a smart design.
Quote:
Originally Posted by ProtegeManiac View Post

This is the DAC chip; what happens to the analog signal until it leaves that chip, particularly the analog output section, might still introduce noise and coloration. And then there's the rest of the system until it hits your eardrums.
Well analogue measurements from a lot of DACs are still outputting perfectly flat responses from 0.1-20kHz and beyond, so it seems like there shouldn't be a difference with them? (well, some are dropping less than 1dB below about 30Hz)
Quote:
Originally Posted by ProtegeManiac View Post

So basically the market - that is, the preferences of people buying all the gear - are an important factor. What's more, what ultimately is "flat" isn't just because listeners want something colored. What a microphone can measure in a speaker or headphone, or the entire system through these, ultimately can still be a problem if eardrums don't have as flat a response as a microphone - it may have dips in the bass, or the -3db point may seem too high; or it can have peaks in the treble; etc. Even if there's nothing wrong with your eardrums human hearing is biased to some frequencies, which is why for example some people will hate the Sun opamps, chalk slipping on the blackboard (or aotherwise any scraping on it), then seek out the "smooth Wolfson."
It's not a DAC's job to tailor the frequency response to your preferences though - that's why there are so many different headphone designs out there. A DAC's job is to turn the digital input signal into a perfect analogue recreation of that - and it seems that there are a number of DAC chips and DAC products that can accomplish this now.

So if the DAC measures perfectly flat, and keeps the noise floor below the threshold of audibility, is there really anywhere to go from here if you can't get a flatter frequency response, or reduce noise any further?

Assuming I pick something which uses a good DAC implementation, and measures well on the analogue output stage, aren't they all essentially going to sound the same? It's not like we need to increase the bit-depth or frequency response further than we have now.
Edited by StudioSound - 2/22/13 at 12:42pm
post #4 of 4
Quote:
Originally Posted by StudioSound View Post


Well I am wanting to use an external DAC for my PC. The problem is that without some kind of delay option in the DAC, audio will be out of sync. That's fine for music, but not video. I'm not looking for a HT Receiver because they are huge boxes with crap headphone outputs, and all I'm looking to drive is a pair of headphones, not speakers.

HDMI would be really convenient because the current spec transmits audio sync data, and would save me running any extra cables.
 

 

There's really no way around it; since DAC devices designed for 2ch audio don't take video into account, none AFAIK have HDMI - that means they also don't integrate the kind of processing circuit for sync-ing video and audio streams. Not even all car audio processors have that kind of sync - the Pioneer I have in my car will only sync drivers to each other so sound from all individual drivers will arrive at my ear as much as possible at the same time (set properly the vocals are dead-center on the dash, and with proper aiming the image of the soundstage will be close to a normal one at home). AFAIK only the high-end Alpine F1 processor can function both as surround audio time alignment+video sync and multi-driver audio processor, and it doesn't have HDMI either.

 

As for their "crap headphone outputs" you can get a receiver with preamp outputs then match the gain, however the retarded thinking from manufacturers is that you either buy a basic processor with an amplifier inadequate for complex speaker loads (like Dynaudio) or they give you a nice processor with a good amp, but that's the one that gets the preamp outputs - which means you pay more just to have a more disposable processor guarantee that you can always use your beefier amplifier. And it's bigger and heavier too.

 

You could check this out though when it's available - it's still not desktop-size but it's just a little over half the size of a typical receiver. You could shoot them an email though if it has A/V sync, I can't find it in the list of specs (although these days I still assume all processors should have that feature).

 

 

Quote:
Originally Posted by StudioSound View Post

I was actually thinking along the lines of the Benchmark DAC2, because it seems to be essentially a perfect implementation of the Sabre DAC, at which point it seems like you would never have to upgrade again if it measures perfectly flat? (at least within the range of human hearing)

But if I am only using the PC as a source, it seems like the O2+ODAC might be all I need - though the analogue output is not quite as good, and I don't see any way of delaying that - there are toslink/coax delay boxes available, and toslink from a soundcard would allow me to take advantage of headphone virtual surround options when gaming.
 

 

Actually that would be the best way to do it - have one DAC for 2ch then have a surround processor for your headphones. While you're at it, why not just get a gaming headset, and just manually switch between Hi-Fi 2ch DAC and that on Windows? Those come with a USB soundcard that can do basic surround processing, that way you don't wear down the earpads on your Hi-Fi headphones, since worn out pads can drasticaly alter the sound. If you've ever read how people debate about how HD600s sound dark to a lot of people and not to the fans who use solid state amps, what's really going on is 1) the people who don't like it are likely to have tried them on worn pads, 2) it's not always just the choice between SS and tubes that make them sound a certain way, but those who strongly prefer tubes might be more tolerant of their pads' wear and tear.

 

BTW I'm also going to need surround sound soon but I've got the luck to have a separate desktop computer and a spare room for a surround system, which I'm setting up just to make full use of the HDMI on the mATX gaming rig my brother handed down and my laptop whichever I'm using. But even if I didn't have the spare room to house speakers and a receiver in, I'd still just have a separate headset+soundcard for games, given the $60 for my HD600's earpads can just buy me a new Creative gaming headset. I actually gave my cousin one last Christmas when I realized how ****ty his computer audio was after blowing his money on the processor and GPU (some 2.0 speakers from an old office).

 

As to which DACs and surround headphone systems specifically, if you get the ODAC and the run of the mill headsets with processors, both will run off USB so that might be a problem for you in case you might need the same ports for other things (like external HDDs,  peripherals, etc). But then again if you don't have the soundcard yet you can save money. But in case you wil just get some kind of external soundcard with a delay processor that isn't bundled with a gaming headset, you should get an amplifier with at least two inputs, that way you can have both processors hooked up to the same amplifer and you just flick a switch on the amp.

 

Quote:
Originally Posted by StudioSound View Post

It's not a DAC's job to tailor the frequency response to your preferences though - that's why there are so many different headphone designs out there. A DAC's job is to turn the digital input signal into a perfect analogue recreation of that - and it seems that there are a number of DAC chips and DAC products that can accomplish this now.

 

Yes, I agree - unfortunately there are too many people who will disagree with this etysmile.gif

 

Quote:

Originally Posted by StudioSound View Post

So if the DAC measures perfectly flat, and keeps the noise floor below the threshold of audibility, is there really anywhere to go from here if you can't get a flatter frequency response, or reduce noise any further?

Assuming I pick something which uses a good DAC implementation, and measures well on the analogue output stage, aren't they all essentially going to sound the same? It's not like we need to increase the bit-depth or frequency response further than we have now.

 

If you hook up measuring equipment to the analogue outputs of the DAC, then they all sound the same in theory. However you can have such problems as some having a different output impedance or voltage, ditto for the input impedance of the amps - so basically even the amp needs to be chosen carefully, although personally the effects aren't necessarily anything I'd lose sleep over. Heck even the cable can probably introduce color to the sound, problem is some people don't like using free software EQ but will spend hundreds if not thousands of dollars in, broadly speaking, "accessories"* when in all likelihood it's jsut the headphone's or speaker's frequency response to begin with.

*I don't think we should go into further detail about that or somebody's going to jump in here firing in all directions, then the mods will shut down this thread.

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