Sound and Vibration

When a speaker cone moves forward, it compresses nearby air. When it moves backward, it produces a region of lower pressure. Those alternating pressure changes travel outward.

The air does not travel from the speaker to your ear as one parcel. Individual particles oscillate around their positions while energy and information propagate through the medium.

Frequency counts cycles per second. One cycle per second is 1 hertz.

For a simple steady tone, increasing frequency generally raises perceived pitch. A4 is commonly tuned to 440 Hz. A5 is 880 Hz and A3 is 220 Hz.

Pitch is a perception, so it is not identical to a frequency reading. Spectrum, duration, level and listening context can affect what pitch the auditory system hears.

Very slow repetitions are heard as separate events. Faster repetition can fuse into a tone with a perceived pitch. The transition depends on waveform, level and listener; roughly 20 Hz is a useful orientation, not a switch shared by every sound and ear.

Use the slider near its low end. Listen for both repetition rate and pitch-like fusion rather than trying to find one universally correct threshold.

Amplitude describes the size of the pressure variation. Increasing it raises physical sound level.

Loudness is the listener's experience. It also depends on frequency, duration, spectrum and hearing sensitivity. Equal amplitude at 50 Hz and 3 kHz will not necessarily sound equally loud.

Decibels use a logarithmic scale because sound pressures and intensities cover an enormous range. A decibel value also needs a reference: dB SPL, dBFS and gain readings do not mean the same thing.

At about 20 C, sound travels through air near 343 metres per second. Wavelength equals speed divided by frequency.

Long bass wavelengths interact strongly with room dimensions. This is why small studios can have large low-frequency peaks and nulls.

A periodic waveform repeats. Its spectrum commonly contains a fundamental and components related to that repetition rate.

Noise is aperiodic or statistically irregular. It can still have spectral shape: white and pink noise differ in how energy is distributed across frequency.

Many instruments combine both. A flute note has a pitched periodic body plus breath noise; a snare combines resonant modes with broadband noise.

Play 440 and 443 Hz together. Their relative phase cycles in and out, producing three amplitude beats per second.

Phase describes position within a cycle. Identical waves aligned in phase reinforce; opposite polarity can cancel under ideal conditions. With microphones, delays vary by frequency, producing partial reinforcement and cancellation across the spectrum.