From the Desk of Art Noxon

Art Noxon is a fully accredited Acoustical Engineer with Master of Science degrees in Mechanical Engineering/Acoustics and Physics. A Professional Engineer since 1982, he is licensed in Oregon to practice engineering in the public domain with the specialty area of acoustics. A prolific inventor, he developed and patented the iconic TubeTrap, the original corner-loaded bass trap/treble diffuser, 150 other acoustic devices, and counting. Lecturer, writer, and teacher of acoustics, he has presented 7 AES papers, numerous magazine articles, white papers and blogs. He is president of Acoustic Sciences Corporation, the company he founded in 1984.


Putting the Art in Articulation

This week we look into the effect of poor articulation on tonal transients. These are sonic events that help to give instruments their "voice" and provide the intimacy and impact that make live music events so captivating.

After all, the pinnacle of high-end music reproduction is achieving the convincing illusion that "you are there!"

Mix Engineers: without properly hearing the transient content of the original recording, your final mix will lack the detail and power that you intend.

A condensed version of Arthur Noxon's article Articulation and the Small Room follows (edited for brevity). 

A musical line...

is characterized as a rapid staccato of complex tone bursts. Music, then, is a set of musical lines, overlaid and intertwining one another. The basic element of this woven fabric of music is the tone burst. The acoustic descriptor that relates to musical articulation may well be the tone burst, indeed a rapid staccato of bursts. Figure 1 shows several tone bursts, each separated by a dwell time. We use here a 50% duty cycle: 60 ms on and 60 ms off.
 
Figure 1: Waveform Representation of Modulated Tone Bursts

For analysis...

we only desire measurement of the signal envelope and the faithfulness of its modulated transmission. Figure 2 shows the source test signal as seen by a dB meter. If each burst is clean and each dwell period quiet, the dB meter output will alternate between loud and quiet levels. The signal rises in the presence of a burst and falls during the dwell time.
 
Figure 2: SPL vs Time Representation of Modulated Tone Bursts

A closeup of consecutive tone bursts...

shows substantial acoustic energy can occupy the dwell period. Figure 3 shows four bursts in 0.8 seconds played and recorded in a real room. Notice how the bursts are deformed. What used to be a sharp attack, flat sustain and abrupt decay has been turned into a pulse that has lost distinctive features.

Ramps, both up and down, take the place of the sharp attack and decay of the articulate signal. The sustain does not hold flat, it is foreshortened by the ramping transitions. In this inarticulate space, the room mumbles, slurs and often will “double-tongue” the rapidly gated signal. Distorted attack transients will obscure the unique character of instruments and timing of the rhythmic event.


Figure 3: Waveform Representation of Modulated Tone Bursts in a Real Room

Equally important is the subjective aspect

The auditor in a precision listening setting can play the test signal over headphones and hear the rapid, clean staccato of tone bursts whose frequency is slowly varied. The auditor expects the room acoustic to play this signal accurately. By removing the headphones and listening to the same signal in the playback room, defects in the transmission path become quite audible.

Figure 4: A Happy Listener Casually Enjoying a HiFi System.  Next Step: TubeTraps!

A Faithful Rendition

The obvious next question is: how to remove the defects?

  1. Let's see... behind door #1... buy a new amplifier? Bzzzzz!
  2. Ok, behind door #2: install new interconnects? Bzzzzz!
  3. Ok, behind the last door: install acoustic control devices to reduce the running reverberant noise floor in your critical listening space? Ding ding ding--we have a winner!