The bass turn-over frequency is nominally

when maximum boost is chosen. The inflection points (the

frequencies where the boost or cut is within 3 dB of the final

value) are for treble and bass

Increasing the values of C2 and C3 decreases the turnover

and inflection frequencies: i.e., the Tone Control Response

Curves shown in Typical Performance Curves will shift left

when C2 and C3 are increased and shift right when C2 and

C3 are decreased. With C2 = C3 = 0.0082 µF, 2 dB steps

are achieved at 100 Hz and 10 kHz. Changing C2 and C3 to

0.01 µF shifts the 2 dB per step frequency to 72 Hz and

8.3 kHz. If the tone control capacitors size is decreased

these frequencies will increase. With C2 = C3 = 0.0068 µF

the 2 dB steps take place at 130 Hz and 11.2 kHz.

LOUDNESS

The human ear has less sensitivity to high and low frequen-

cies relative to its sensitivity to mid-range frequencies be-

tween 2 kHz and 6 kHz for any given acoustic level. The low

and high frequency sensitivity decreases faster than the sen-

sitivity to the mid-range frequencies as the acoustic level

drops. The LMC1982’s loudness function can be used to

help compensate for the decreased sensitivity by boosting

the gain at low and high frequencies as the volume control

attenuation increases (see the curve labeled “Gain vs Fre-

quency with Loudness Active”).

The LMC1982’s loudness function uses external compo-

nents R1, R2, C4 and C5, as shown in

Figure 5, to select the

frequencies where bass and treble boost begin. The amount

of boost is dependent on the volume attenuator’s setting.

The loudness characteristic, with the volume attenuator set

at 40 dB, has a transfer function of

The external components R1 and C4 can be eliminated and

pin 10(19) left open if bass boost is the only desired loud-

ness characteristic.

DS011028-7

FIGURE 3. System Block Diagram Utilizing the External Processing Loop (One Channel Shown)

DS011028-8

FIGURE 4. The Tone Control Amplifier

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