Derek Bowers | Jan 24, 2012

Early radio receivers and record players nearly always had a knob marked “tone,” which was usually a crude low-pass filter with some form of severity adjustment. At best, these controls could partially compensate for bass loss caused by poor speaker baffling. More sophisticated controls were developed for more modern equipment, including the bass/treble (Baxandall) controls, parametric equalizers, and graphic equalizers.

Nevertheless, a single-adjustment tone control often can be useful for fine balance adjustment or where multiple controls are impractical or unnecessary. A simple version of such a control provides a symmetric response that is flat at the center of the adjustment range (Fig. 1).

早期的无线电接收器和录音机几乎总是有一个标有“音调”的旋钮，通常是一个粗糙的低通滤波器，带有某种形式的重度调整。充其量，这些控制可以部分补偿由不良的扬声器隔板造成的低音损失。更复杂的控件因更现代的设备而开发，包括低音/高音（baxandall）控件、参数均衡器和图形均衡器。

然而，一个单一的调节音调控制对于精细的平衡调节，或者在多重控制不实际或不必要的情况下，通常是有用的。这种控制的简单版本提供在调整范围内中心平坦的对称响应（图1）。

这个简单电路允许为需要精细的平衡调节或多重控制不太实际的应用提供单电位器调节音调控制。

Moving the control in one direction simultaneously boosts the treble and cuts the bass until about 5.5 dB of boost and 23 dB of cut are obtained. Moving the control in the other direction boosts the bass and cuts the treble in an identical fashion. Figure 2 shows the typical curves obtained from 20 Hz to 20 kHz with a 1-kHz center frequency, for the lower half and upper half of the control range, respectively.

在一个方向上移动控制时会同时提高高音和切掉低音，直到获得约5.5 db的提升和23 db的衰减。向另一个方向移动控制时可以提高低音，并以相同的方式降低高音。图2分别显示了控制范围下半部分和上半部分在中心频率为1-kHz的情况下，从20 Hz到20 kHz的典型曲线。

Naturally, for stereo, the circuit would be duplicated and VR1 substituted with a dual, ganged component. Since the circuit is purely passive, it is easy to insert in the signal chain. However, it must be preceded by a low impedance (below 100 Ω) and followed by a high impedance (more than 250 kΩ) for best results. Under these circumstances, insertion loss (at center) approaches 6 dB.

自然地，对于立体声，电路将被复制，VR1将被一个双联组件替代。由于电路是纯无源的，所以很容易插入信号链。但是，为了获得最佳效果，必须先使用低阻抗（低于100Ω），然后使用高阻抗（高于250 kΩ）。在这种情况下，插入损耗（中心）接近6db。

Since this is a purely passive circuit, all component values may be scaled without affecting the ac transfer function. With lower resistor values (and higher capacitor values), the signal-to-noise ratio improves, but the circuit requires a lower impedance to drive it. The values shown represent a good compromise. Overall signal-to-noise ratio in a 20-kHz bandwidth is about –113 dB referenced to 1 V rms with the control in the center position.

由于这是一个纯无源电路，因此可以在不影响交流传递函数的情况下比例缩放所有元件值。电阻值越低，电容值越高，信噪比越高，但电路需要更低的阻抗来驱动。显示的值代表了一个很好的折衷方案。控制处于中心位置时，20 kHz带宽中的总信噪比约为-113 dB（参考1 V rms）。