FIG. 1

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.

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

This tutorial refers to the mp-3 audio track linked here. File size is 5 MB.

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 Tube Trap ^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 Tube Trap ^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.

Tube Trap, for the articulate listening room.

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.

For a small fee, ASC can analyze your MATT Test results and provide a report along with recommendations for acoustic improvements. You provide us with a recording of the MATT Test in your room and we'll take it from there.