Loudness Calibration

To compensate for the changes in human perception to varying volume levels, Loudness applies a predetermined filter curve to the signal in response to output volume values. As volume is lowered, perception of certain frequencies is progressively diminished, returning to a more flat response as volume is increased. Therefore, Loudness will boost those frequencies to the highest degree at low volume, decreasing that boost as volume increases.

Inserting Loudness into the signal chain can be a set-and-go operation. Loudness can also be fine-tuned by ear, or calibrated using an SPL meter and either pink noise or program material. First, it is important to set up the basic gain structure of the system. See topic, Loudness Dialog Overview, for more information on the controls used to calibrate Loudness.

Setting Input and Output Gain Structure

Before calibrating loudness, set up the system gain structure (see, Optimizing Audio Levels for more information). A pre-recorded track of pink noise (played through, e.g., a DVD player) or a signal generator with pink noise is preferable for this purpose; otherwise, program material may be used (using material that you are familiar with is recommended).

The pink noise should be recorded at −20dBFS. Or, set the signal generator to output −10dBu, then set the input gain in the DSP Configurator so that the input meter reads −20dBFS. If using a recorded source and the player has an output level setting control, set the output of the player to its maximum, or 0dB of attenuation. For program material, set the input level to meter at approximately −15dBFS, with peaks safely below 0dBFS.

Make an audio tie from the source to the speakers that will carry program material in the room to be calibrated. With the basic gain structure is now set up, Loudness can be calibrated using an SPL meter or by ear. (Loudness can also be set using an SPL meter, then fine-tuned by ear.)

Calibrating Loudness

To calibrate loudness, use a sound pressure level meter set to "C" weighting.

1. Set the Loudness processor to Bypass.

2. Place the meter in an average (but somewhat prominent) listening location.

3. Generate pink noise, or start your program material playback.

4. Measure the SPL in the room.

5. In the Loudness dialog, adjust the slider until the value in the "SPL" readout box matches the reading on the SPL meter.

Theoretically, calibration can be performed with the output channel Volume and/or Post Gain level set to any comfortable listening level, but a relatively loud volume (well above the ambient noise in the room) that can be easily measured is preferred. Loudness is now calibrated. Disengage Bypass to hear the compensation.

An alternate method is, with the Compensation Adjustment slider in its default center position and the output channel Volume fader at 0dB (100% volume), adjust the amplifier until the SPL meter reads 90dB. Loudness is now calibrated. This method works if 90dB is an acceptable amplifier/volume limit for the room.

Setting Loudness "By Ear"

When setting Loudness by ear, it is also essential that the system gain structure be set up first. Sit in an average (but somewhat prominent) listening location.

1. Set the Loudness processor to Bypass.

2. Set the output Volume fader in the DSP Configurator to a relatively quiet listening level. Filter compensation from the Loudness processor is most prominent at low listening levels. Use program material that you are familiar with, set to the levels described earlier.

3. The Calibrate slider should be set to 0/center point. Disengage the Loudness bypass switch. You should experience a moderate enhancement to the program material, with more accentuated bass frequencies (below 500Hz), and more brightness in the high frequencies that carry harmonic content (above 7kHz). You may engage and disengage the bypass switch in order to "A/B" the difference between loudness off and on, respectively.

4. To experiment with less loudness compensation, move the Loudness Compensation slider to the left, in the direction of Less. For more loudness compensation, move the slider to the right toward More.

5. Any adjustment you make to the Loudness Compensation slider will carry through to all listening levels. Set the output Volume fader in the DSP Configurator to a relatively loud listening level.

6. Engage and disengage the Bypass switch in order to "A/B" the difference between loudness off and on. At a loud listening level, this difference should be minimal, or barely perceivable.