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Good converters vs poor converters, what is each doing differently?
Old 18th February 2015
  #1
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Lance Lawson's Avatar
 

Good converters vs poor converters, what is each doing differently?

Assuming that converters are the most important link between the analogue domain and the digital domain how is a better converter better crunching the numbers that are stored on the hard drive? How would a string of numbers differ for an identical sample of sound between a great, good and poor converter. Since a poor converter can play a wave file made from an excellent converter they must be extremely close in character.
Old 18th February 2015
  #2
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Converters are the only link between the analog and digital domains.

First there are different converter chips themselves, the ADCs and DACs manufactured by the big suppliers like TI and Linear. There are many ways to skin a cat and conversion is no different, so there are dozens of different types of conversion. In audio we generally only see one type, sigma-delta converters. Of these, there are thousands of models to choose from, though not nearly as many will be appropriate for audio (in terms of sample rate and word length). Of those that are audio-friendly, so to speak, each will have its strengths and weaknesses in terms of SNR, linearity, cost, etc. You can look through the datasheets of various models to see what this is all about, though for the most part there's not a giant disparity between chips still in production.

So this is one place where interfaces can differ in quality: the quality of the chips themselves. But because high quality chips are not expensive, the biggest difference between the quality of interfaces is in the design of the analog circuitry surrounding the converter chips, including the power supply. The PCB layout is especially important if the designer wants to achieve the specs of the chips, and this requires experience and the willingness of management to go through multiple revisions to get it right. If all that is well-engineered (and they get the digital filtering right, which shouldn't be a problem), then the quality difference between interfaces approaches that of the chips themselves, i.e., minimal.

The differentiators then become features, number of I/O, and of course cost.
Old 18th February 2015
  #3
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Tal Black's Avatar
 

Quote:
Originally Posted by Lance Lawson View Post
Assuming that converters are the most important link between the analogue domain and the digital domain how is a better converter better crunching the numbers that are stored on the hard drive? How would a string of numbers differ for an identical sample of sound between a great, good and poor converter. Since a poor converter can play a wave file made from an excellent converter they must be extremely close in character.


'Close in character'? Depends upon the definition of 'character'.

I recently moved from MOTU 2408MK3 to Apollo and the difference is striking.

The first thing I did was export stereo mix tracks, for a song that was done and in the can, to the new rig (all new interface, DAW and computer) and mix it down by memory.

The drums were all on one stereo track. This is where I was expecting trouble. I thought cymbals would all poke out. Turned out the cymbals and the snare were fine but the kick popped out markedly. So did the heavy guit rhythm tracks. I actually had to fix two rhythm strokes that were fractionally early but not really audible in the prior mix. Turns out that the air around the kick, bass, heavy guit as well as the frequency definition or roundness are noticeably more audible thru the Apollo

While the overall sound of the Apollo is darker or more high dampded, the lows and low mids (100hz to 1.5k) are more audible or forward. The result is that it is much easier to know when a mix is done and without over pushing the highs. That is what really struck me.

Also a very odd thing to me is that when I EQ a guitar sound (no amp, monitoring thru A7's) The 3k shelf is cut rather than boosted, the bass shelf has half the cut as previously and the mid setting is less cut as well; and I'm done in a quick two minutes. Previously it took a half hour of going back and forth before I 'settled' resolving to work it out in the mix. this is the same rig I've been using since my Tascam 338 days over twenty years ago.

A convertor is analog and digital. Which stage is doing what I don't know but the differences between MOTU and UA in sum, are, as I said, striking. If you can't make a 'Record' with MOTU you have problems that an Apollo won't fix. But so far recording and mixing and listening are far easier with the Apollo. Given the relatively low price of the Apollo I can't fathom that the sound/conversion could be very different from the MOTU...but...well there we are.
Old 18th February 2015
  #4
Quote:
Originally Posted by bogosort View Post
Converters are the only link between the analog and digital domains.

First there are different converter chips themselves, the ADCs and DACs manufactured by the big suppliers like TI and Linear. There are many ways to skin a cat and conversion is no different, so there are dozens of different types of conversion. In audio we generally only see one type, sigma-delta converters. Of these, there are thousands of models to choose from, though not nearly as many will be appropriate for audio (in terms of sample rate and word length). Of those that are audio-friendly, so to speak, each will have its strengths and weaknesses in terms of SNR, linearity, cost, etc. You can look through the datasheets of various models to see what this is all about, though for the most part there's not a giant disparity between chips still in production.

So this is one place where interfaces can differ in quality: the quality of the chips themselves. But because high quality chips are not expensive, the biggest difference between the quality of interfaces is in the design of the analog circuitry surrounding the converter chips, including the power supply. The PCB layout is especially important if the designer wants to achieve the specs of the chips, and this requires experience and the willingness of management to go through multiple revisions to get it right. If all that is well-engineered (and they get the digital filtering right, which shouldn't be a problem), then the quality difference between interfaces approaches that of the chips themselves, i.e., minimal.

The differentiators then become features, number of I/O, and of course cost.
Clearly and succinctly put.
Old 18th February 2015
  #5
Registered User
Quality of power supply and the case, shielding, layout and quality of components surrounding the chips all greatly affect the noise level, both internally generated noise and shielding from outside noise, and filtering out AC ripple. These things come at a price. Plastic boxes do not cut it.
Old 18th February 2015
  #6
Registered User
Quality of power supply and the case, shielding, layout and quality of components surrounding the chips all greatly affect the noise level, both internally generated noise and shielding from outside noise, and filtering out AC ripple. These things come at a price. Plastic boxes do not cut it.
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