# Thoughts on A/D conversion.



## Jeff Flowerday (Jan 23, 2006)

I've been doing some research on analog to digital conversion. Of course all the various priced recording interfaces have built in A/D converters of varying quality. There are also the high end stand alone options, that the pros rave about.

What has everyone used/tried. What did you like and what was the best you heard even if you couldn't afford it.


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## Pneumonic (Feb 14, 2008)

I have used a bunch of A/D/A units over the years. Put them through their paces doing ADC work (recording and needledropping) along with DAC work at audiophile level. 

I have used Aardvark, EMU, M Audio, ART, Benchmark, Lynx, Lavry, Universal Audio, and Metric Halo. All colour the sound differently so really preference is a VERY personal thing. My favourite is the one I currently use, a Metric Halo (ULN2). Most neutral sounding converters I have heard. My buddy has the ULN8 and it's even better.


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## Guest (Jun 1, 2010)

I've only used M-Audio, Aardvaark and Apogee. The Apogee is head and shoulders above the other two. The pre's + A/D/A on the Duet are as transparent as any I've ever encountered.

FWIW: "colouring" is going to come from the pre's, not the ADC in high end boxes. Every high end box samples with enough bits and frequency to be undetectable by the human ear. Most use the same chips even for conversion.


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## ronmac (Sep 22, 2006)

I have heard and used a good number. The Metric Halo gear is very, very good. 

Unless you absolutely need the best (not many of us do) there is not much to be gained by going from mid-level converters (RME, MOTU, etc.) to the real high end stuff. If I were building a new system I would upgrade a lot of things (room treatment, monitors, mics, pres, instruments) before I ever considered going for better ADA conversion.


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## Jeff Flowerday (Jan 23, 2006)

iaresee said:


> I've only used M-Audio, Aardvaark and Apogee. The Apogee is head and shoulders above the other two. The pre's + A/D/A on the Duet are as transparent as any I've ever encountered.
> 
> FWIW: "colouring" is going to come from the pre's, not the ADC in high end boxes. Every high end box samples with enough bits and frequency to be undetectable by the human ear. Most use the same chips even for conversion.


Take the pre's out of the equation and the analog portion prior to the ADC and after the DAC can color still, no? From what I've read it's the quality of the analog circuit portion that makes the high quality devices stand out, not so much the actual ADC or DAC chip like you said. Though clock and power supply seem to be heavy topics as well.

My limited experience:
I've only really tested Presonus and RME side by side from a DAC standpoint. The RME was night and day better sounding, IMO. Fuller and warmer with a much better stereo image and instrument seperation. It's harder to compare the ADC because of too many different variables prior, you really don't what's is making things sound different.


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## Pneumonic (Feb 14, 2008)

ronmac said:


> I have heard and used a good number. The Metric Halo gear is very, very good.
> 
> Unless you absolutely need the best (not many of us do) there is not much to be gained by going from mid-level converters (RME, MOTU, etc.) to the real high end stuff. If I were building a new system I would upgrade a lot of things (room treatment, monitors, mics, pres, instruments) before I ever considered going for better ADA conversion.


True but, oh man, you should hear,say, a MH ULN8 compared to my ULN2. Night and day and the ULN2 is excellent on its own.


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## Pneumonic (Feb 14, 2008)

Jeff Flowerday said:


> Take the pre's out of the equation and the analog portion prior to the ADC and after the DAC can color still, no? From what I've read it's the quality of the analog circuit portion that makes the high quality devices stand out, not so much the actual ADC or DAC chip like you said. Though clock and power supply seem to be heavy topics as well.
> 
> My limited experience:
> I've only really tested Presonus and RME side by side from a DAC standpoint. The RME was night and day better sounding, IMO. Fuller and warmer with a much better stereo image and instrument seperation. It's harder to compare the ADC because of too many different variables prior, you really don't what's is making things sound different.


Indeed, it's all about the implementation of the circuitry versus the actual chipsets themselves. 

When I did my comparisons (digitizing my pristine vinyl for example) with A/D/A's I did so with system integrity in place on the recording and playback sides. The only thing that changed were the ADC's. With a resolving enough system on the playback side, and an ear trained to listen for subtleties, the differences in sound quality can be significant, oftentimes staggering. I learned the hard way, having to re-do over 400+ albums because I initially used an inferior, albeit well reviewed and respected, ADC. Live and learn they say ......


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## Guest (Jun 2, 2010)

Jeff Flowerday said:


> Take the pre's out of the equation and the analog portion prior to the ADC and after the DAC can color still, no? From what I've read it's the quality of the analog circuit portion that makes the high quality devices stand out, not so much the actual ADC or DAC chip like you said. Though clock and power supply seem to be heavy topics as well.


I guess I can turn that around and ask: what do you think comes before the ADC and after the DAC? Answer: not much. On the DAC side there's lots of room for variance implementing the output amplifier that drives the signal on the cable, but right after the DAC it all looks pretty much the same. Going in to the ADC there's a conditioning opamp and a filter that rolls off frequencies that are above the nyquist frequency so you don't get any odd artifacts. Most, I'd even make a pretty educated guess here and say all, of the manufacturers are using the reference implementations of the pre-sampling circuits for their chosen chipsets. Why? Because there's really only one way to skin that cat.

Clock stability is important, but it is so incredibly cheap to get an ultra stable oscillator for the frequencies modern samplers run at that everyone has them. This is really, really not high tech any more. Power design is actually where you might see the most variance from manufacturer to manufacturer since that tends to be a completely in-house and unique thing. So there's certainly some noise floor on the table where manufacturers can vie for superiority -- trying to implement the quietest ground plane and most ripple-free power lines possible in their devices.



> My limited experience:
> I've only really tested Presonus and RME side by side from a DAC standpoint. The RME was night and day better sounding, IMO. Fuller and warmer with a much better stereo image and instrument seperation. It's harder to compare the ADC because of too many different variables prior, you really don't what's is making things sound different.


I'd definitely agree with that. Way easier to compare the output using a reference signal. So after all that I'd say: buy with your years. If your music sounds good on it, that's the one for you. The nice thing is there's a freaking plethora of choice out there right now for interfaces. Set yer budget and SHOP!


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## Jeff Flowerday (Jan 23, 2006)

Pneumonic said:


> Indeed, it's all about the implementation of the circuitry versus the actual chipsets themselves.
> 
> When I did my comparisons (digitizing my pristine vinyl for example) with A/D/A's I did so with system integrity in place on the recording and playback sides. The only thing that changed were the ADC's. With a resolving enough system on the playback side, and an ear trained to listen for subtleties, the differences in sound quality can be significant, oftentimes staggering. I learned the hard way, having to re-do over 400+ albums because I initially used an inferior, albeit well reviewed and respected, ADC. Live and learn they say ......


Yah, I'm on my third time with some of my needle drops, though not 400 albums maybe 30 total. I only rip stuff that isn't available on CD. Even though I find most of my current drops sound better than the CD version, when comparing particular songs that are on compilations only.


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## Pneumonic (Feb 14, 2008)

iaresee said:


> I guess I can turn that around and ask: what do you think comes before the ADC and after the DAC? Answer: not much. On the DAC side there's lots of room for variance implementing the output amplifier that drives the signal on the cable, but right after the DAC it all looks pretty much the same. Going in to the ADC there's a conditioning opamp and a filter that rolls off frequencies that are above the nyquist frequency so you don't get any odd artifacts. Most, I'd even make a pretty educated guess here and say all, of the manufacturers are using the reference implementations of the pre-sampling circuits for their chosen chipsets. Why? Because there's really only one way to skin that cat.
> 
> Clock stability is important, but it is so incredibly cheap to get an ultra stable oscillator for the frequencies modern samplers run at that everyone has them. This is really, really not high tech any more. Power design is actually where you might see the most variance from manufacturer to manufacturer since that tends to be a completely in-house and unique thing. So there's certainly some noise floor on the table where manufacturers can vie for superiority -- trying to implement the quietest ground plane and most ripple-free power lines possible in their devices.


The biggest sonic differecnes in ADC's exist due to design woes at the buffering/PSU and filtering stages before the (delta) modulation of the signal takes place. Poor, inadequate, or no, high frequency filtering in the early stages cause interference with subsequent delta modulation causing audible distortions. It's amazing how many reputable designs skimp on the processing power required to adequately design proper filtering. And while analog buffering isn't a complicated matter, the almighty $ rears its ugly head allowing/forcing? some designs to skimp on the buffer stage thereby not requiring more costly power supplies. And let's not forget sheer design laziness on the part of the engineers who implement such designs. With all of the chip based filters in today's commercial ADC chipsets, too many enginners can't be bothered spending time, energy and effort (read R&D costs) bettering the filters that the silicon guys have come up with on chip. Even some very basic external programming done to these on chip filtering pays huge sonic dividends.


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## Pneumonic (Feb 14, 2008)

Jeff Flowerday said:


> Yah, I'm on my third time with some of my needle drops, though not 400 albums maybe 30 total. I only rip stuff that isn't available on CD. Even though I find most of my current drops sound better than the CD version, when comparing particular songs that are on compilations only.


I drop for unavailabiluty reasons too as well as for sonic betterment and preservation reasons. I also love to "remaster" titles to sound the way I wish them to sound. It's a VERY addicting (read time consuming) hobby. But, for me, also extremely enjoyable. But I'm an audiophile junkie of the highest order .... or so says my wife.


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## Guest (Jun 2, 2010)

Pneumonic said:


> The biggest sonic differecnes in ADC's exist due to design woes at the buffering/PSU and filtering stages before the (delta) modulation of the signal takes place.


Everyone is using the same opamps for buffering. They're all cheap relative to the cost of the units with similar impedance and low noise characteristics. Filtering is, as I said before, done by the reference design specs and the same from unit to unit. I'd even suspect most are relying on the onboard filtering and buffers on the ADC. There's no reason to build outside the box here. You can't do anything better.



> Poor, inadequate, or no, high frequency filtering in the early stages cause interference with subsequent delta modulation causing audible distortions.


See above. Everyone uses the same filter setups recommended by the ADA manufacturers. There's nothing to gain going off reference.



> It's amazing how many reputable designs skimp on the processing power required to adequately design proper filtering.


The filtering done to remove anything above the Nyquist frequency is done in the analog domain. I'm not sure what you're talking about here when you say processing power.



> And while analog buffering isn't a complicated matter, the almighty $ rears its ugly head allowing/forcing? some designs to skimp on the buffer stage thereby not requiring more costly power supplies.


There are definitely differences in how power is delivered to the opamp from manufacturer to manufacturer. No question about that. The rest is all the same. From your Creative Labs Soundblaster up to your Metric Halo the opamps and filter components are on par.



> And let's not forget sheer design laziness on the part of the engineers who implement such designs.


Well, now you're just getting insulting. 



> With all of the chip based filters in today's commercial ADC chipsets, too many enginners can't be bothered spending time, energy and effort (read R&D costs) bettering the filters that the silicon guys have come up with on chip. Even some very basic external programming done to these on chip filtering pays huge sonic dividends.


What else do you think can be done other than a simple low pass filter for the Nyquist frequency? My experience says: nothing. Yours? This has nothing to do with R&D costs, it has to do with useless work -- what's on chip is perfectly adequate for all scenarios. And if you buy an ADC without a built in opamp and filter section you're going to follow the reference design and build with the same components everyone else is building with because a top notch opamp and filter section will put you back about $2 in parts.

I'm not saying their aren't differences. The preamps and line drivers are completely vendor-specific. There's some room for vendor-specific improvements in power supplies to the ADC and DAC chips, keeping that signal noise-free is helpful in reducing bit errors and injecting noise at the buffer. But that's it. When you buy Metric you're buying their pre's and line drivers (and the software drivers) over another brand, not their ADC, DAC sections.


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## Pneumonic (Feb 14, 2008)

Nope, never seen a cct designer take the easy way out either by choice or by direction <wink> Plenty of variables in the implementation of ADC circuits which can alter the sound we hear. Right down to the terminations employed.

I actually bought my ULN2 for it's A/D/A and look at the mic pre's as a feature tossed in. I'm running it as the primary digital source in my main audio rig in boot state standalone without MIO software. Ditto the UA 2192 that the MH replaced. And the Aardvark's prior to it.

FWIW. My original point is that all of the A/D/A's that I have used have sounded different. And they were the ONLY variable changed in the equation. So, for me at least, they don't all sound the same. Not anywhere near so.


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## Guest (Jun 2, 2010)

Pneumonic said:


> Nope, never seen a cct designer take the easy way out either by choice or by direction <wink> Plenty of variables in the implementation of ADC circuits which can alter the sound we hear.


Can you give me some examples?



> Right down to the terminations employed.


Terminations? Where?


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