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Rational Acoustics Smaart v7.1
Editor’s Note: Steve submitted this as his
regular “On the Digital Edge” column for the
January issue of FOH but, as it is a pretty extensive
look at the nuts and bolts of a much-used
software program, we are running it as a Road
Test instead. Same stuff, different header.
Getting Smaart RT
The latest revision of Rational Acoustics’
Smaart is v7.1 which runs under Mac OSX (10.5
or 10.6) as well as Windows 7, XP, or Vista. Rational
Acoustics recommends at least a 2 GHz
dual-core processor and Smaart is compatible
with CoreAudio, WAV or ASIO audio drivers. I
ran Smaart on a MacBook 2 GHz Core 2 Duo/4
GB RAM with Digi 002R and MOTU Traveler
interfaces. If you’ve never used Smaart, it’s
worthwhile reviewing the resources available
from the Rational Acoustics web site, particularly
the PowerPoint presentation and basic
setup guide. Reading these documents while
following along with your system can cut
down the learning curve, and since there’s a
lot to learn about Smaart, this idea is… well…
smart.
The Interface RT
Rational Acoustics incorporated many
improvements to the interface of Smaart v7.1,
including a “Capture All” command that stores
all active measurement traces and an improved
trace filing system. A major change is
that this version supports simultaneous measurement
of multiple channels. Other changes
will be discussed below.
Smaart’s primary modes (Real Time and
Impulse Response) include time and frequency
domain measurements, but first you need
to set up your hardware in the audio dialogue.
When Smaart recognizes your interface, it appears
on a menu of available I/Os. You can then
set sample rate, bit-depth (16 or 24) and apply
your own names to the inputs and outputs
(nice for managing multi-channel systems).
Smaart played very well with my Digi 002R at
sample rates of 44.1-, 48- and 96 kHz, though
it does not support 88.2 kHz (which I don’t see
as a problem). I cannot say the same for my
MOTU Traveler, which Smaart did not like very
much. Sometimes Smaart would recognize
the Traveler, and other times — typically after
changing the sample rate — it would not.
Averaging and Weighting RT
Inputs are organized and added into
Groups under the Group Manager, where
you’ll find parameters including averaging
and weighting. Version 7.1 is the first to support
multiple channels, enabling simultaneous
measurement of, for example, console
output, a mic at FOH, another mic in the balcony,
etc. Active channels are viewed “overlay”
style; clicking on an input in the Control Strip
brings its trace to the front of a window. It’d be
nice if you could tile the screen into separate
windows for each trace (e.g. four windows of
RTA, each displaying a channel).
One of the few gripes I have with Smaart
is that weighting is neither displayed nor accessible
from the Control Strip, though it is
indicated in the trace area. Figure 1 shows the
Smaart Spectrum (RTA) function. Note that the
Control Strip on the right (detailed in figure 2)
displays the averaging but not the weighting,
which I consider essential [Editor’s note:
the numeric readout at the top of the Control
Strip shows weighting for the dB meter,
not the analysis tool]. The Spectrum display
can show RTA, Spectrograph or both via split
screen (figure 3). All of the screens look great
and are easy to read, but one thing I did not
like is that when you zoom in or out, the scale
of the screen changes, but the resolution of
the grid does not (i.e., you can zoom in as far as
you want, but the grid is still divided into 6 dB
steps). To select an area of a window for zoom,
right-click and drag on it or, on a one-button
mouse, hold + and click
and drag.
Other Functions RT
At the top of the Control Strip is a numeric
indicator that shows dBFS, dB SPL (Smaart
provides calibration for SPL) or dBLEQ. dBLEQ
is capable of long-term SPL monitoring over
a user-defined period (we went as far as six
hours), with user-defined increments. A “logging”
feature creates a text file of these measurements
showing minimum and maximum
SPL as well as the actual SPL at a given date
and time. It’s a very useful tool, especially in
venues where the neighbors make noise complaints.
Smaart’s Transfer Function allows comparison
between a reference signal and the
post-process version of that signal in an audio
system, measurements which reveal interesting
traits. An example is shown in figure 4,
the Transfer Function of a monitor system in
a small control room. This was measured by
generating pink noise (from Smaart’s signal
generator), splitting it and sending it directly
into Smaart on the Reference channel and
also to the monitors. A measurement mic
picked was connected to the Measurement
channel. This comparison involves a delay between
the two signals (the Reference signal
does not travel through the air, and therefore
reaches Smaart faster). To maintain accuracy,
there must be compensation for the delay.
Smaart has an automatic delay finder that calculates
delay, even while you are moving the
mic around the room. It worked perfectly. In
Fig. 4, the lower two windows show Transfer
Function. The middle trace (green) shows frequency
versus phase difference while the bottom
window shows magnitude (green) versus
frequency difference between reference and
measurement mic. The bottom also shows
“Coherence” in red (a discussion of coherence
is beyond the scope of this article, but it points
toward reliability of accumulated data). In this
particular instance we are in Live IR Mode, so
Smaart added a third window at the top of the
screen with amplitude versus time difference
between the two channels. The green spike at
approximately 5.6 mS and the smaller bump
roughly one mS later provide insight as to why
the green trace in the Phase window looks so
erratic (phase problems and comb filtering),
and also why the red trace is not as coherent
as we might like.
Impulse Response RT
Impulse Response measurement is always
tricky, because if measurement parameters
are not set carefully, data acquisition
is inaccurate. The setting for Time Constant
(TC) must be long enough to include the
entire decay time of the system under test.
When capturing the impulse response of a
room with a decay time of 1.5 seconds, a TC
of 682 mS yields inaccurate data, because
Smaart is not given enough time to “hear”
the entire decay. The solution is increased
TC, which also increases the FFT (Fast Fourier
Transform). Processing time increases
with increased TC, so one benefit of using
Fig. 1
The Smaart Spectrum (RTA) function
Fig. 3
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Split screen view of the Spectrum display.
The Transfer function of a monitor system in a small control room.
shorter TC is that you see the results faster.
Smaart provides TC settings ranging from 2
and 10922 mS, with corresponding FFT sizes
and averaging to improve reliability.
There are a couple of minor things that
I’d like to see tightened up in Smaart. In addition
to the aforementioned difficulty with
the Traveler interface, there is an issue with
using the MacBook’s built-in I/O. Smaart recognizes
the I/O, but at times, attempting to
use it prompts a message stating “Failed to
Start Device.” The folks at Rational Acoustics
are working on solutions to those issues.
Nit-picks aside, there’s no doubt that
Smaart is an extremely powerful software
Road Test
By SteveLaCerra
Fig. 2
tool, in particular for touring sound companies
and installers. It takes a bit of time to become
familiar with all of the capabilities but
should be considered essential for anyone
requiring critical evaluation of audio system
performance. It’s also an excellent teaching
tool, providing a means of illustrating a variety
of acoustic phenomena. A new license
for Smaart runs $895; upgrades from earlier
versions range from $450 to $650.
Steve “Woody” La Cerra is the tour manager
and FOH engineer for Blue Öyster Cult. E-mail
him at woody@fohonline.com.
2011 JANUARY
A closer look at the
Control Strip in Fig. 1.
Fig. 4
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