Texas Instruments TAS3002 Dynamic Loudness Contour, 4.9.1Loudness Biquads, 4.9.2Loudness Gain

4.9 Dynamic Loudness Contour

The necessity for applying loudness compensation to playback systems to compensate for the fact that the ear perceives bass and treble less audibly at low levels than at high ones has been established since the first data was published by Fletcher and Munson in 1933.

There are many equal-loudness contours in publication, like Steven’s contours, Robinson and Dadson contours. Some have even reached the acceptance level of ISO recommendation.

The TAS3002 device has a simplified loudness contour algorithm that diminishes the effect of weak bass at low listening levels. Since contour has volume level dependency, the user must define the relation between the gain of the contour circuit and the volume level.

Figure 4−3 is a block diagram of this circuit.

Volume

BiquadGain

Figure 4−3. Dynamic Loudness Contour Block Diagram

The loudness contour is activated by sending an activation command via I2C from an external device. Optionally, a contour gain command can be sent by an external device to provide tracking with the system volume control.

4.9.1Loudness Biquads

Loudness biquad filters for the left and right channels are independently programmable via I2C. Their subaddresses are 21h and 22h, respectively. The digital filters are written as five 24-bit (4.20) hex coefficients for each channel.

4.9.2Loudness Gain

Loudness gain values for the left and right channels are independently programmable via I2C. Their subaddresses are 23h and 24h, respectively. The gain values are written as one 4.20 hex coefficient for each channel.

4.9.3Loudness Contour Operation

When the frequency of the loudness contour is determined, a digital filter must be developed. Then, the gain of the filter is determined. These values are placed in the storage area of the system controller (microcontroller) and sent to the TAS3002 device when it is desired to activate the loudness contour.

If it is necessary to change the frequency or gain of the contour, new gain and filter coefficients are sent by the system controller. This function is performed normally when the volume control is changed (that is, more volume, less contour). The gain of the loudness contour filter then tracks the volume control.

The loudness contour biquad filters are provided in addition to the seven equalization biquad filters.

See Section NO TAG for programming instructions.

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