Musical articulation is one
basic requirement that must be met by nearly every audio system.
This test has been developed to record and display the "fast
tracking" capability of the audio chain. The graph below
(Fig.1) is the analysis of the test signal itself. If you
listen to the test signal over headphones you will hear what
the fully articulate signal really sounds like.
In the following diagrams,
the test signal has been played and recorded at various listening
positions. Fig.2 and Fig.3 show how the test signal was actually
received at each position. Some portions of each graph will
look and sound articulate. This is recognized by sections
with a wide vertical "zig-zag" pattern similar to
the articulate signature of the test tape printout.
FIG.2 - ORIGINAL SIGNAL
FIG.3 - AT LISTENER POSITION
Areas of poor articulation
are evidenced by sections of small amplitude zig-zag. The
room slurs and garbles the sound of the discrete test tones.
Make a copy of each original recording and play it over headphones
while studying the printout from the same test. You will quickly
learn how the variations in intelligibility as shown in the
printout are really very audible.
Discussion
of the Test
The basis of the test signal is a very slow
sine wave sweep. It starts at 28 Hz and rises up to 780 Hz,
then it drops back down to 28 Hz. It is easier to read the
printout when presented in this symmetric form. The linear
frequency vs time curve is triangular in shape and takes about
80 seconds to complete.
The slowly changing pure tone signal is then
chopped, alternately turned on and off at some particular
rate. For the typical music playback system, the test signal
is gated at 8 Hz, eight distinct tone bursts per second. A
50% duty cycle is used so each tone is played for 1/16 second
and is followed by 1/16 second of silence.
This measures the fast response, dB level
curve at the listening position. Specifically, it measures
how loud each burst is and how quiet each silent period becomes.
The test analysis circuitry can follow as much as a 20 dB
drop in level during a 1/16 second of silence. Articulation
is the ability of the room to distinctly sound out each audio
event.
Two things are noticed in room response curves
made from this test. The sound levels may not always drop
away during the quiet periods. They may not always rise during
the sounding of the tone. In either case, the vertical amplitude
swing of the graph will be small and the room is garbling,
and slurring the otherwise distinct tone bursts.
The second feature to observe from this test
are the changes in overall sound levels. The test signal is
EQ'd flat and the vertical zig-zag follows a flat baseline.
When the test tone sequence is played into a room, the room
resonances and absorption coefficients that change with frequency
cause overall sound levels to vary. The zig-zag articulation
signature follows this hilly terrain. If the articulation
signal were to be smoothed out we would see that its baseline
is the traditional "slow sine sweep" room response
curve.
When the room is acoustically treated to better
develop articulation, two things will be noticed from this
test. The room response curve will tend to flatten out, as
if the room has been somewhat EQ'd. The second feature will
be increased articulation. This is evidenced by a wider swing
of the vertical zig-zag line over a greater percentage of
the frequency range tested. The "ideal" articulate
room measures wide and flat with this test.
Short Tutorial
for the Articulation Demo Tape
A short tutorial tape has been prepared to
illustrate the effects that the listening room has on the
perception of the MATT, an articulation test signal. Here
we introduce the tutorial tape and display hard copy printouts
to accompany listening to the actual signals on the tutorial
tape.
The articulation test signal is a rapid series
of tone bursts held steady at 8 bursts per second. The tone
of each burst is different, on a sliding scale. This demo
tape presents only the last half of a real test. It fades
in when the tone is about 780 Hz, in the middle of the test
and follows the signal down to 28 Hz, its lowest frequency.
Each tone burst sequence lasts about 45 seconds. Altogether
there are 6 parts to the demo tape.
The room where the tape was made is a heavy
wall, 2000 sq-ft listening room, built for research and testing
at the ASC factory. It has a concrete floor with sheetrock
walls and ceiling. All acoustic recordings were made in a
professional manner with a crossed pair of mics for stereo
and placed at the listening position. The speakers were placed
in a typical hi-fi setup. The 6 tracks are as follows:
1. Original signal
2. Lightly treated room
3. Well treated room
4. Bare room
5. Original signal
6. Well treated room
Accompanying each track is an introductory
comment by the recording engineer that identifies the track.
Here we present the printout of each test. The audio signal
is passed through a dB meter circuit so the level changes
associated with each burst can be tracked.
It is clear that playback articulation is
a direct function of acoustic conditioning in the last link
of the audio chain, the listening room.
Test 1.
Original signal
"The first sequence is the music articulation
test recorded directly from the test oscillator."
Test 2.
Lightly treated room
"The next sequence is the music articulation
test recorded in a room with light acoustic treatment."
Test 3.
Well treated room
"The next sequence is the music articulation
test recorded in the same room with a complete TubeTrap TM
acoustic treatment system."
Test 4.
Bare room
"The next sequence is the music articulation
test recorded in a bare room."
Test 5.
Original signal
"The music articulation test recorded
directly from the test oscillator."
Test 6.
Well treated room
"The music articulation test recorded
in a room equipped with a complete TubeTrap TM
acoustic system."
Demo the Defect
- Room Articulation
The MATT (Musical Articulation TEST TONES)
contains an audio test signal designed to test the fast-tracking
ability of the listening room. The room acoustic is the last
link in the audio chain. It is responsible for most of the
deterioration of playback quality. A simple, quick and very
effective A/B demo to this effect is available with the MATT
signal.
The clean signal is best audited over a set
of headphones. The signal path distortion is minimal with
this type of acoustic coupler. Once the rapid set of distinct
ascending and descending tone bursts are familiar, take the
headphones off and listen to the room acoustic playback version
of the same signal.
During room playback a number of different
effects will be audible.
Ta-Ta-Ta-Ta, the sound of an articulate
group of tone bursts. There will be usually some 8 to
10 clean bursts in such a group, lasting about one second.
A typical room will have only a few of articulate groups
of signals in the 75 second test.
Tattle-Tattle-Tattle-Tattle, the tell-tail
sound of the room's double-tongue response. Large spans
of the tract will have this sound. Notice that the tonal
pulse rate is really twice that of the real signal. Too
much energy occupies the dwell period of the test signal.
Toodle-oodle-oodle-oodle, the sound of
the garbled room. Notice that it is a softer, less impacted
sound. It's close to a slurred, double-tongue response.
Tathump-Tathump-Tathump, is a more accurate
presentation of the TA-TA. The "thump" is the
turn-on and turn-off transient effects. This subtle transient
coloration becomes totally inaudible with anything but
articulate room playback. The thump is a damped 45 Hz
ringing with only 2 oscillations of presence following
each burst transition.
These effects, all distinct, audible and measurable
are controlled by the room acoustic. More importantly, the
"demo the difference" experience leads the auditor
to observe firsthand the significance of the acoustic interconnect.
Then the auditor will realize and accept the impact the listening
room has on the otherwise accurate, fast-tracking audio chain.
Audio is no longer satisfied with launching
a clean wavefront through grill cloth and calling the job
done. The room acoustic is clearly the last and weakest link
in the upscale audio chain. Now, you can demo the defect and
upgrade the interconnect.
TubeTrap, for the articulate listening room.
ASC MATT Test Analysis
For a modest fee ($50 + $25 per test), ASC
will analyse your MATT Test data and make suggestions to help
you deal with acoustic weaknesses in your room. You provide
us with a recording of the MATT Test in your room and we'll
take it from there. The MATT signal is available on the Stereophile
Test CD 2 (track 19) and on the PROSONUS Studio Reference
Disc (track 50). Or, download
the Mp3 file and burn it to a CD. To save the file
to your computer, right-click (Windows) or control-click (Mac),
then choose the save option. The diagram below illustrates
a typical MATT test set-up.
No gain control or equlization should be
used.
Use an omni-directional microphone with
a flat frequency response and place at the listening position.
Do not stand behind or near the microphone.
It needs to be out in the open.
Record onto a cassette or DAT recorder.
Label the tape before it is sent
to ASC for processing. A sketch showing the test set-up
would also be helpful.
