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Converter Crazy - Part 1
From A/D to D/A. Let’s face it, without them we would
be nothing. Bridging the gap between two radically different
worlds, converters are arguably the most important step in
the digital recording chain. But with so many options on
the market these days, what do you look for in a quality
converter? Why would you even need an additional A/D or D/A
converter if your Pro Tools interface already has them built
in? This week we will look at some of the basics of digital
audio as it relates to the conversion process and discuss
where Pro Tools users might fit in when deciding on whether
or not to add a new converter to their system. Since this
is such a huge topic, and always fun to chat about, I would
like to break this discussion into 2 parts. This week we
cover converter basics, next week I will dive into some real
world scenarios and set-ups, so stay tuned!
A Crash Course In Converters
If you are unfamiliar with the term “converter” as
it relates to the digital audio world, allow me to bring
you up to speed. First things first, we are analog beings
and we like analog things. Our body’s senses process
continuous signals that ebb and flow like an ocean’s
waves, infinite in their complexity. Computers on the other
hand deal in absolutes, seeing the world as a finite number
of 1s and 0s. An A/D (analog to digital) converters job is
to transcend these two worlds by converting continuous signals
(in the form of electrical current) to a series of discrete
values (1s and 0s), in attempts to capture this infinite
world of analog information in a finite space. Why a finite
space you ask? Because in the digital realm, hard drives
can only hold so much information and processors can only
process so many bits of data. So you see there has to be
some sort of “bottom line” for audio existing
in the digital world, and it is the converters job to sort
this whole mess out. Just remember, an A/D converter “digitizes” analog
signals into the digital world, while a D/A converter un-digitizes
them back out again when returning to the analog world.
So how does this A/D converter transport our audio signals
from one world to another? The process is called sample-and-hold.
Sampling is like taking a snapshot of the sound wave at regular
intervals. If we measure the value of the continuous waveform
at enough points along the curve, we can accurately recreate
an audio signal as a set of discrete samples. The sampling
rate determines how many snapshots, or samples of the sound
wave are taken in one second. The higher the sampling rate,
the more samples taken per second. A converters bit depth
determines the resolution of each sample or snapshot taken
and is reflected in the amount of dynamic range that can
be represented within a digital signal (roughly 6dB per bit).
As bit depth increases, more data is needed to store each
snapshot because more detail is used in measuring the value
of that sample. The bit depth and sampling rate of an audio
CD is 16bits-44.1Khz, or 44,100 samples per second at 16bits
per sample. This is by no means a comprehensive discussion
of digital audio theory, and I encourage anyone who wants
to learn more to do a Wikipedia search on the topic. Believe
me, a strong foundation in these basic concepts will help
you make smart decisions when shopping for a new digital
converter.
Options for Pro Tools
First off, your Pro Tools system already has A/D and D/A
converters built into the interface, regardless of whether
you have and Mbox, 002, 96IO, etc. So depending on your workflow
an additional A/D or D/A converter may not be necessary.
Some Pro tools Systems allow the use of add on converters
through digital I/O and some don’t, but most interfaces
support only specific kinds of digital connections. Before
you go looking for a new converter check out my handy table
below to find out which Pro Tools interfaces can use additional
digital converter/s and what format/s they support. Note
that this table shows the number of digital ins and outs
possible and unless noted, this is in addition to the exiting
analog ins and outs on the interface.
Notice I have not included the HD interfaces on this table
as both the 192io and 96io support the most common forms
of digital connections (S/PDIF, ADAT Optical, AES/EBU). The
192io also supports TDIF connections. Since there are just
too many M-Powered compatible devices to list, check out
the specs on your unit. Currently the following M-Audio interfaces
support additional digital I/O: Audiophile 192, Audiophile
2496, Audiophile USB, Delta 1010, Delta 66, Fast Track Pro,
Firewire 1814, Firewire Audiophile, Firewire 4/10, Project
Mix, and Transit.
Do you really need an extra A/D or D/A converter?
But why would anyone want to add an additional converter
to his or her current Pro Tools setup? There are a few reasons
actually. The first reason that comes to my mind when people
say they need to add additional A/D or D/A would simply be
for more ins and outs. Many Pro Tools interfaces include
extra digital inputs that often go unused and when paired
with an appropriate A/D or D/A converter users can expand
the functionality of their current interface. So if you need
some extra inputs on your 002 to record that whole drum kit
and the rest of your band at the same time, an additional
converter may be the ticket.
The second thing that comes to mind when I hear people talking
about A/D or D/A converters is quality. Even though they
essentially accomplish the same thing, all converters are
not created equal. Because the conversion from analog to
digital (and back again) is by no means lossless, the more
accurately a converter can sample your incoming audio, and
the more accurately that audio can be recreated when it makes
its trip back to the analog world, the better your digital
recordings will come out in the end. Bottom line, some converters
just do a better job then others.
But before I start a “mine is better then yours” argument,
it is important to know that the quality difference in converters
can be very subjective. People swear by their brand of A/D
like they swear by Coke or Pepsi. So when it comes to choosing
a new converter it is very important to avoid the hype and
really use your ears. The good news is that today’s
digital converters have never sounded better. With 24-bit
as the new standard and tremendous improvements in filter
design, even the cheapest converters on the market today
perform leagues better then the most expensive brands did
10-15 years ago. So before I get a dozen emails asking “Brian,
are my Mbox converters bad? Do I need to get new ones?” do
your self a favor and listen. Can you hear a difference?
Does your workflow and budget warrant costly, premium conversion?
Just know that the converters in todays systems are all really
good compared to only a few years ago, and things are only
going to get better.
So which is it, A/D or D/A? While most add-on converters
these days provide both A/D and D/A in one unit, some do
not. If you record a lot of audio, good A/D may be more important
since you only get one chance to capture that analog signal
accurately. If you find yourself doing more mixing or using
all virtual instruments in your workflow, excellent D/A may
be more important for accurately monitoring your outgoing
signal. Ideally a system would have a balance of both quality
A/D and D/A, but you may be able to save money and purchase
a higher quality unit by going with one or the other. Always
remember to consider your budget, and try to maintain a balanced
system. You can have the greatest A/D converter money can
buy but it will do you no good if your guitar won’t
stay in tune or your mic preamp is noisy. A DAW is only as
good as the weakest link in the chain.
Coming up!
Stay tuned. Next week I will share an example of connecting
an external converter to a Pro Tools system, talk about what
features to look for in a new converter, discuss the various
digital formats and point out some specific options that
Pro Tools LE users have to expand their I/O.
Pro Tip: Fine-tune your faders
Ever go to move a fader or a pan just ever so slightly and
you end up pushing it about 10 dB’s more then you wanted?
Well for this week’s Pro Tip I have a simple trick
that you can use to slow down fader movements and use while
fine-tuning your automation.
To slow down fader/pan motion
- Hold down the Command Key (MAC) or the Control Key
(PC) while you adjust a fader or pan slider with your mouse.
The
fader will now move in .1dB increments instead of the usual
.3dB’s (Pan will now move in 1% increments).
- Let go of the modifier key at any time to return to
standard fader resolution.
Hint: You can also use this modifier key when moving or
trimming automation breakpoints making small fractional changes
a breeze.
Pro Tools Tidbits:
- SSL’s Duende now works on PC (v1.5)
- Native Instruments has released updates to Kore (v1.1), Kontakt
(v2.2) and Reaktor (v5.1.2)
- Antares Avox is now Intel Mac compatible.
If you have a Pro Tools related question that you would
like me to take a shot at answering or have any feedback,
please send it to brian@audioMIDI.com.
I will do my best to select the questions that seem to stump
the most people.
As always, stay tuned to the audioMIDI.com eNews for the latest reviews and new product info.
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