The MATT test signal is the brainchild of acoustical engineer Art Noxon, president and founder of Acoustic Sciences Corporation (ASC) and the inventor of the Tube Trap, a cylinder shaped high performance bass trap with a built-in treble range diffuser. The MATT test signal was developed as an acoustic performance listening test. It is closely related to speech intelligibility tests and often referred to as a musical intelligibility test. It was copyrighted in 1986 and converted to freeware on April 10, 2018. We'd like to thank Art Noxon for kindly helping us in drafting this page.
MATT stands for Musical Articulation Test Tones. It was created to help the listener of an audio system to hear and measure the degrading effects of room acoustics on the audio signal. Later, after making some acoustic adjustments in the room, the improved listen-ability of the room can also be heard and measured. By recording the Before and After sound of the test at the listening position the A/B comparison is memorialized.
The original test is made up of a frequency sweep which ascends from 28 Hz to 780 Hz and descends back down to 28 Hz. The sweep signal is gated, turned on and off (50% duty cycle), at a rate of 8 times per second. Between each 1/16th second tone burst is a 1/16th second period of silence which is about 40 dB quieter than the tone burst in the test signal.
The basis of the test signal is a very slow sine wave sweep that is turned on and off rapidly, as to produce a train of tone bursts at increasing and then decreasing frequencies, each burst being followed by silence. If you listen to the test signal over headphones you will hear what the fully articulated or dynamic signal sounds like. Playing that same signal in a room will sound different. And, how different depends on the quality of your listening room.
As the frequency changes the MATT signal excites various reflections and resonant modes in your room that linger long enough that they fill sound into the silent portions of the MATT signal. This unwanted sonic lingering translates into a loss of articulation that is audible in poor rooms. A more detailed explanation on how the test works is available here.
As Art Noxon says, “poor room acoustics turns yodeling into gargling”. The curious thing about garbled sound is that it has the same tonal or harmonic content as the good sound. What is different between good and garbled sound is the loss of being able to hear the modulation in the sound, how it changes over time, its dynamics.
The results of this test can be recorded at the listening position and at a later date played into a sound level strip chart recorder to see the dynamic room response curve when measured in dB over time. Since the sweep frequency is steady over time, 16 Hz/second, the time scale of the strip chart can be converted into a frequency scale. But remember, this is first and foremost a listening test, which is why we like to include it here on AudioCheck.net
|ASC Original (1986)|
Listen to the test signal over headphones first, to hear what the actual signal sounds without any interference from room acoustics. You don’t have to listen to the whole test, just enough to get the idea. Then, listen to the same signal as it is being played through your speakers. When the test tone sequence is played in a room, the frequency-dependant room reflections, resonances and absorption will cause overall sound levels to vary. In addition to demonstrating the frequency response of your room, the MATT also demonstrates how garbled or slurred your room sounds, its dynamic clarity or articulation, as the frequency of the sound is changed.
If your room is well treated, there will be very little loss in musical articulation and the frequency response will be fairly smooth. The test signal should play like a repeated Ta-Ta-Ta-Ta, just like the headphone version. In most somewhat treated rooms the articulate signal effect can be achieved only in groups of a dozen or so bursts, bandwidths of 30 to 40 Hz followed by a more narrow bandwidth, maybe 10 Hz, of somewhat inarticulate tone bursts.
This test will help you to hear the frequency ranges of dynamic blur which will help you choose the frequency range of the acoustic treatment you want to be looking for. After you get some acoustics you still have to figure out where to place it. Try setting it up in a location that seems to make sense and listen to the MATT test to see what happened. Move it to another position and repeat the MATT test and so on until you get the acoustics located where it does the most good. The general advice for bass traps is to start with bass traps in the front corners of the room. Add bass traps along the side walls in the front 1/3rd of the room. Add bass traps to both the front and back wall to help with the major room modes that belong to the length of the room.
Before you get too carried away with bass traps and treble range sound panels you might try changing the position of your speakers to see what that does. Most room acoustic problems involve the interaction between the speaker position and the geometry of the room. MATT test will help you find the most neutral position for your speakers in the room.
Here’s an interesting anecdote. The original signal was all generated with analog gear, and the gate that was used had abrupt rise and decay times resulting in audible clicks. Nowadays, one would compute that signal digitally, and ensure that each burst is properly windowed to avoid the clicking transient. But, after years of use, it appeared that those clicking artifacts actually made the test better, for subjective listening. Why? Because the onset transient tapping sound, the clicking artifact that accompanies the tone bursts are actually the first degradation of sonic accuracy that can be noticed.
When a room or more often when the front half of the listening room goes into reverberation, the lingering sound spills into and obscures the sonic detail in the attack transient of the next tone burst. This loss of attack transient detail is the most sensitive loss in musical clarity and occurs long before the actual garbling effect becomes noticeable. Then, upon the proper sizing and placement of bass traps and treble panels, the ability to hear the clicks returns. So, these clicks (aka attack transients) proved to be a desirable feature as hearing them acknowledges excellent room articulation
|AudioCheck Version (2018)|
Following discussions with Art Noxon - the inventor of the test - we decided to re-create the signal, by today's standards, here at AudioCheck. This new version has been digitally synthesized. While the clicking (turn-on transient) could have been eliminated it has been kept faithful to the original signal, except in this new MATT signal sequence every tone burst has the same attack transient, unlike the original test signal where only some of the tone bursts had the turn-on attack transient.
The goal is to end up with a better subjective signal (see previous section). The gate is extreme, and acts like like an on/off switch (square windowing). The gating frequency is the same as the original (8Hz) and so is the sweep (28-780Hz). We aimed at recreating the exact same signal, but with a trick : the gate will only activate at the closest zero-crossing points of the sweep tone. The idea is to keep the abrupt raise times of the gate, while avoiding the uncontrolled and possibly loud clicking that is produced when one chops a waveform arbitraritly in its cycle.
|MATT By Ear (0-200Hz)||MATT By Ear (0-2000Hz)|
As we resynthesized the MATT test, we took the opportunity to create a couple of variants that will make your subjective assessment even easier. With these new versions, you will be able to find the problematic frequencies values simply by count, without any additional equipment required, or if any, just a stopwatch.
We keep the exact same philosophy, just changed the sweep characteristics. The first test scans all frequencies from 0 to 200Hz, in a 20-second time span. That makes a scanning speed of exactly ten Hertz per second. The other file ranges from 0 to 2000Hz, also over a period of 20 seconds. That makes 100 Hz per second. So, if you count from zero to twenty, one number per second, while the test plays, you are actually giving yourself a hint what frequency is currently playing. Multiply your counting by 10 or 100, and you'll have the equivalent in Hz.
|HD MATT (0-100Hz)|
At last, we provide a super high resolution MATT test, for the lower frequency range, that one with a scanning speed of 1Hz per second. In other words, that file takes 100 seconds to scan frequencies from 0 to 100Hz. Note, frequencies below 15 Hz are totally inaudible, but these were included to make the counting easier. The gating signal is slightly different, to accommodate the slower sweeping time and the increased frequency definition. It now varies from 1Hz at the beginning of the test to 8Hz at the end. The longer gaps at the lower frequencies were needed to better hear the adverse effect of your room in that range.
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