In an RC oscillator, frequency is inversely proportional to resistance × capacitance: smaller R or C raises pitch

In both toy clocks and the 74C14 Schmitt Trigger oscillator, frequency is determined by the RC time constant: f ≈ 1/(RC), where R is resistance in ohms and C is capacitance in farads. Doubling either R or C halves the frequency (drops pitch one octave); halving either doubles the frequency (raises pitch one octave). The capacitor value determines the pitch range that the variable resistor sweeps through. Very small capacitors push the frequency into ultrasonic or clock ranges; large capacitors push it into sub-audio metronome territory. This relationship governs both toy clock hacking and scratch-built oscillator design. It is also why a single 74C14 chip with six RC pairs can cover sub-audio to ultrasonic using different capacitor values.

Examples

74C14 oscillator with 100kΩ and 0.01μF: ~1600 Hz. Replace resistor with 1MΩ pot: covers ~160 Hz to ~16,000 Hz. Replace capacitor with 10μF: same pot covers 0.16 Hz to 16 Hz (metronome to slow audio).

Assessment

A 74C14 oscillator uses a 10kΩ resistor and 0.1μF capacitor and sounds at 1 kHz. What capacitor would you use to bring it down to 100 Hz with the same resistor? What resistor value brings it to 100 Hz with the same capacitor?