Now that you have downloaded the MATT and played it through your system, you have a better sense of which regions of the audio range are good or bad in your room. But maybe you want to get more specific, and identify the narrow bands of inarticulation so you can fix them. Whether you are a mixing wizard or a discriminating listener, you need to hear things right.
The Reference Signal
The source signal for the MATT provides a very large dynamic range, beyond that which is perceptible by the human hearing mechanism. Therefore our analysis software maxes out at about 25 dB of articulation. Anything greater than this is unnecessary, a bit like a 5th supercharger on a Bugatti Veyron.
See the output of analyzing the reference signal below. Let’s set expectations realistically: NO ROOM ever looks like this!
The top chart shows the signal vs. frequency (literally, voltage-vs.-time) and is the original method of analysis. The “thickness” of the signal demonstrates a very high level of articulation as the level dynamically changes about 25 dB between each tone burst. This occurs in the absence of room resonances and reflections.
The second chart shows the upper and lower envelopes. The green curve essentially shows the frequency response of your system. The purple curve essentially shows the resonance response of your room, or the running reverberant noise floor. The vertical gap between these two curves shows the articulation in any given frequency band.
Finally, the third chart shows a higher resolution signal vs. frequency focusing on the subwoofer and bass range. In all cases, the frequency scale is linear because the tone sweep is linear. This is how we avoid the limitations of FFT/spectral conversions. The time and frequency data maintain accuracy throughout the entire test.
How good is good?
The charts shown below are good examples of the thick dynamics that a good room can provide to your audio playback. An ASC AttackWall was used by Mr. King in his recording studio.
How bad is bad?
See how thin and wispy the level-vs.-time display is? The highly jagged green line shows a plethora of cancellations and peaks as the room chaotically echos and rings. The purple line shows a HUGE noise floor in Mr. Fudd’s room-caused by acoustic anomalies. Surprisingly, the subwoofer range is not too bad. The subs must have been placed properly at the 29% points.
Show Me the Numbers!
We know you love metrics!
The classic graphical method of displaying the MATT provides a great overview and also very narrow band information. But it lacks the single number that tells you how good your room really is. Since our analysis software is generated in-house, we have been tinkering with different ways of “scoring” your room’s articulation.
Articulation vs. Frequency
This version shows tells you how your room is doing in each frequency band. For example, Mr. Fudd has very poor articulation in the 165 Hz band and many more bands throughout the upper bass and mid range, with an average score of 7.2 dB across the test range. Anything below 10 is “poor.”
On the other end of the performance spectrum, we see Mr. Maverick’s control room scoring off the charts. Every range besides the lowest subwoofer octave is fantastic, with an average score of 18 dB across the test range. Slightly better subwoofer positioning should bring the average over 20, into the “Hall of Fame” range.
Weighted Average Portion of Test Bandwidth
The other version of quantifying the overall system performance tallies the number of bursts exhibiting certain dynamic performance and plots this on a chart comparing dB articulation and percentage of test bandwidth. This tells you what portion of the audio range (sub through midrange) is performing at poor, good, excellent, or Hall of Fame levels.
Mr. Fudd’s cousin submitted the test shown below. Not particularly good. We think he should install some sound absorbers. Preferably, Isothermal TubeTraps in the 13×3 and 16×3 Models. We’d like to see the 50% point above 10 dB, or better.
Now, Lady McTubeTraps knows her acoustics, and the numbers show it. While we are still going to try to increase the dynamic headroom so that the lowest articulation scores are closer to 10dB, those TubeTraps have done a great job fixing the room.
How to Get the Numbers
Hopefully you have made some initial changes to improve the subjective tests described last week. Now, are you ready to take the next step in room design and send your tracks to ASC?