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Digital Audio Converters
Basics of a Quality Signal Path

By TweakHeadz Lab

Getting the maximum sound quality for your home or project studio is our goal.  We all want professional studio sound, right?  Well, pay attention to this article, as I am going to try to show you the most direct path to get there.  As I mentioned on the main page of the site, in tip #1 "Focus on what touches the sound"  Hint:  It's NOT the computer.  The computer just takes your audio in number form and manipulates it.  Plugins too just manipulate the numbers.  So what DOES make a difference?  It's real simple:


Excellent Microphone
+ Excellent Preamp
+ Excellent Converters
+ Excellent Monitors

=Great Sound!


There it is.  It's the critical pathway from the sound you emit in performance to the record of it, i.e., the recording, that ends up on your hard drives to the sound you hear coming out your speakers.  What does a pro studio have that you do not?  They may have several excellently configured pathways from analog to digital and back.  A pro studio has a wide range of microphones, several great quality preamps, typically 8-16 or more A\D converters and a few D\A options and a range of monitors on which to check the work being performed.  The cash outlay for such sonic goodness may be around $20,000, just for these items. 


The Lucid AD9624 is an analog to digital converter.  The company also makes a D\A converter


Of course, a home studio that aspires to professional sound is going to have to take shortcuts.  The idea here is to develop a single 2-channel, super quality signal path going in an out of the recorder.  You start with a handful of excellent mics, get a single (or dual), high quality preamp, add a stand alone analog to digital converter and a digital to analog converter to bypass those on your audio interface, and get an excellent pair of monitors so you can hear and appreciate the goodness.  Any weak link in this chain compromises sound quality.  The quality of your sound will only be as good as the weakest component in this chain. 


Signal Chain:

Microphone -> Preamp -> A\D Converter -> Recorder -> D\A Converter -> Monitors


You'll find articles on all these critical components here on TweakHeadz.  This article focuses on the most hidden elements in the chain:  The Converters.

Whether you are aware of them or not, you already have converters.  Every product that records or processes digital audio has them.  Multitracks, digital effects processors, CD Recorders, samplers and some synths all have them.  The most important ones are the ones you use to record your talent:  the ones on your soundcard or audio interface.  Some of these DACs are really cheap.  Think of the $35 soundcard that may have come with your computer system.  It's converters have to be cheap enough to allow the manufacturer to make a profit.  The DACs might be less than a dollar of the manufacturing cost. 

PreSonus DigiMax FS 8-Channel ADA Converter with Microphone Preamps
Loaded with direct outputs and inserts on every channel, the DigiMax FS is the perfect hardware expansion for your FireStudio 1818 or any digital recording system with optical light pipe expansion capability.
Lucid AD9624 24/96 kHz A/D Converter
A first-class converter for recording, mastering, and post-production: Take your digital recording system to the next level with the addition of the AD9624. This converter bridges the gap between analog and digital equipment with transparent audio conversion. True 24-bit resolution is the best way to record and process all the detail the human ear can hear. The AD9624 supports sample rates of 96kHz, 88.2kHz, 48kHz, 44.1kHz, and 32kHz. What's more, the AD9624's noise shaping function enhances the clarity of low-level material for superior imaging and realism when creating 16-bit masters.  Tweak:  I have this one.  Easy to setup; great meters provides for increased sonic detail with my MOTU 828mk2

PreSonus Central Station Studio Monitor Control Center
The Central Station is the ultimate studio-monitoring interface for the modern digital studio. The Central Station features 3 sets of stereo analog inputs to switch between input sources such as: DAW, mixer, CD/DAT/Tape player, or keyboards/samplers. Two stereo analog inputs feature TRS balanced and the 3rd stereo input features RCA inputs with trim control for level matching of input signals. In addition, the Central Station will accommodate 2 digital inputs via S/PDIF or TOSLINK providing D/A conversion up to 24Bit/192kHz.


What does a converter actually do?

I will keep it basic here.  The Analog to digital converter takes the stream of analog audio and assigns numbers to represent the waveform, and clocks it.  It measures the waveform and divides it into strings of numbers at a bit depth (16 bit, 24 bit, etc) at a sample rate (44,1000, 96,000, 192,000, etc).  All converters, even the lowest you find in computers, can do the 16/44.1 conversion and better audio interfaces can easily do 24/96 or higher.  But the question now becomes how well is this conversion done.  If the converter uses a clock that is less than perfectly stable you can guess that the audio will come out with errors, perhaps even audible clicks and pops. 

The D\A converter does the opposite of the A\D.  It converts the stream of numbers back into an analog voltage that can go to the speakers and be reproduced as sound.  Both are important.  You may have recorded the most beautiful sound in the universe, but if the system can't get it to the speaker, it's like it never happened. 


How to add a stand alone converter

I can hear you.  "I just spent $1100 on an audio interface/ control surface/midi interface system.  Now what do i do?"  Fret not, adding converters is something anyone can do at any time as long as your audio interface or soundcard has some form of digital connectivity, such as s/pdif (coaxial or optical), AES-EBU, ADAT.  To connect any piece of gear via the s/pdif in on the interface is to effectively bypass its converters.  Same going out.  Connect a D\A to the s/pdif out of the system and you have replaced the D\A on the whole system.



Professional converters can be found in Tweak's Audio Pro Shop

apogee Rosetta 200

apogee ensemble

Tweak:  Apogee is known for great sounding conversion.  They make dedicated converters like the Rosetta 200 above.  There converters are also found in their audio interface, the Ensemble, which is designed to work with Logic. 


Cable path for adding 2-channel digital audio converters using s/pdif i/o

Preamp analog out ->
A\D converter (analog line in, digital out)->
audio interface s/pdif in ->
recorder ->
 audio interface s/pdif out ->
D\A Converter (digital in, analog out) ->


As you see, there is really nothing hard about wiring up a 2-channel converter path.  In your recorder, lets say, a sequencer, you simply set the record path to the s/pdif input rather than the analog inputs.  On your master output channel, you select s/pdif out rather than out 1-2.  Everything else works same as before.  To use the superior clock on your new A\D converter, instead of the onboard clock of the audio interface, you make an adjustment in your control panel.  You may have options for internal, s/pdif, word clock, external, system, etc.  Usually, you just select s/pdif so the audio interface uses the converters clock signal.  Since the converter's clock is not compromised by the millions of things that computer's have to do, you'll get audio that is sliced and diced with greater stability and as a result you'll have fewer errors.

You can also add a converter to a Mixer/Soundcard system.  You just patch the converter off the alt-3-4 bus and to the s/pdif input of the soundcard.  That way everything going down your recording bus gets the benefit of better conversion.  If you record track at a time, all your tracks benefit. 


Lynx Studio Technology Aurora 16 16-Channel Digital Audio Converter

The new Aurora line of digital audio converters from Lynx Studio Technology offers unprecedented audio quality and control in single-rack space eight and sixteen channel models. The Aurora 16 features 192 kHz analog to digital and digital to analog conversion with front panel control of all routing and sample rate options. Extended functions in Aurora are accessible via computer with the Lynx AES16 or by infrared using compatible laptops and handheld Pocket PCs. The rear panel has Clock and MIDI In and Out connectors and an LSlot bay, for the optional use of ADAT, Firewire and other audio interfaces.


Can you really hear the difference that converters make?

That takes us back to our equation.  If you have poor monitors, probably not.  If your signal was crappy in the first place due to a bad mic or bad cables or a poor preamp you can bet that stand alone converters will just make a more perfect replica of that crappiness.  However, when you bite the bullet, get nice mics and pres, have solid cables and have the ability to reproduce the sweet on subtle sounds of quality audio on your monitors, then your converters make a difference.  But as usual with high end audio gear, its not the kind of night and day difference you will hear playing a single track, but something that adds up over the process of making several tracks.  One thing that better converters do for you is they help preserve low-level ambient characteristics of a recording.  If your monitors are up to snuff, just play your favorite CDs through a good D/A converter.  For me, I start to hear details i never heard before on my hi-fi system, like the sound of the room the instruments were recorded in, subtle inflections of vocalists and a more human, lifelike quality.  I use the Presonus Central Station as my D\A converter. 

PreSonus Central Station Studio Monitor Control Center
The Central Station is the ultimate studio-monitoring interface for the modern digital studio. The Central Station features 3 sets of stereo analog inputs to switch between input sources such as: DAW, mixer, CD/DAT/Tape player, or keyboards/samplers. Two stereo analog inputs feature TRS balanced and the 3rd stereo input features RCA inputs with trim control for level matching of input signals. In addition, the Central Station will accommodate 2 digital inputs via S/PDIF or TOSLINK providing D/A conversion up to 24Bit/192kHz.  Tweak:  The Central station has an excellent D\A as well as passive electronics controlling volume.  It has dramatically improved what i hear in the studio. 

Summing Up

Remember what we discussed earlier in the Guide.  You can get 90% of the way (some may claim 95%) with off the shelf, good quality music gear.  It's that least 10% that you pay dearly for.  It's exactly that 10% that separates the sonics of the home studio from the pro studio.  Once you have your path, you work on the techniques and skills to drive your audio to perfection.  Choice of mics, mic setup and technique, gain staging, recording level and the ins and outs of processing.  But those topics are for other classes.  Developing a solid, professional signal chain gives you a chance to deliver professional sound at home.



Q) Tweak!  I just got an audio interface and now I find I need converters, preamps, what?!!!  What is going on!

A) Lets be clear.  The converters on most good quality audio interfaces are fine and capable of excellent sound.  You work on your chain when the sound has to be of the highest standard.  Adjust your expectations.  No, one does not get outstanding sound out of a $1000 system.  If it were possible, you can bet that all the pros would be using it

Q) I think i may want a a\d converter, but with two channels, how do you deal with plugging in different gear that you want to record? Can you use it for mixdown too?

A) A 2 channel converter lets you record 2 channels at a time through it.  You can switch its inputs with a common patchbay.  Otherwise you have to do a lot of plugging and unplugging behind each piece of gear.  Alternatively, you could use the alt bus of your mixer, sending only the channels you want to record through the converters.  You could, for example, do analog summing at your console and send the output of the mixer to the audio interface through the a\d converter, ensuring the best conversion you have available.  So with a little ingenuity, you can use your converter for both tracking, analog bouncing and mixdown.

Q) Since I have a system with mediocre preamps and converters do i have to trash the whole thing? 

A) Not at all.  The good thing about building a pristine audio path is that you can add components one by one, and every part of the path is always replaceable.  You can always add another preamp, converters, mics and monitors to any system.  Adding converters only requires that you have digital inputs and outputs that match those on the converters you want to get.



Cool Quote

The chief enemy of creativity is good taste

--Pablo Picasso (1881-1973)  Spanish painter

Discuss digital audio converters at Studio-Central

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Tweak's Articles on Essential Studio Concepts

Hooking Up Audio
MIDI Basics
The Many Functions of MIDI Data
The Audio Interface
Signal Flow Computer-based Studio
Signal Flow of an MPC Hip Hop Studio
Signal Flow of a MultiTrack Studio
Assembling Your Studio Rig
Studio setup in a Nutshell
5 Hot Tips
Building a Quiet Room
Understanding MIDI Interfaces
The War on Hum
Multiple Video Displays
Latency and how to Deal
Word Clock
Everything About Cables
Digital Audio Converters
Bit Depth and Sample Rate
Studio Monitors
Impedance for Musicicans
How to setup a Patchbay
Room Acoustics Basics
Studio Monitors Price List
Acoustic Products
Catalog of MIDI Interfaces



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