Kilohertz to Megahertz

The Nyquist theorem requires a sample rate at least twice the highest frequency you want to capture. Human hearing tops out near 20 kHz, so you need at least 40 kHz. The extra 4.1 kHz provides headroom for the anti-aliasing filter to roll off. The specific number 44,100 was chosen because it factored neatly into the video frame rates of the PAL and NTSC systems used to store digital audio on videotape during early CD mastering.

Kilohertz (kHz) measures oscillation frequency — cycles per second. Kilobits per second (kbps) measures data throughput — bits transferred per second. A 44.1 kHz audio sample rate means 44,100 snapshots per second, but each snapshot may be 16 bits, yielding 705.6 kbps for one channel. The two units describe fundamentally different things: how fast something vibrates vs. how fast data flows.

AM radio was developed first and was allocated the medium-frequency band (535–1,705 kHz) because those wavelengths travel long distances by bouncing off the ionosphere at night. FM came later and was assigned the VHF band (87.5–108 MHz) — higher frequency means shorter range but much better audio fidelity and resistance to static. The allocation reflects both physics and regulatory history.

Yes. A typical dog whistle emits ultrasound between about 23 and 54 kHz — well above the human ceiling of ~20 kHz but within a dog's hearing range, which extends to roughly 65 kHz. Some "silent" whistles do leak a faint hiss that keen human ears pick up, but the dominant output is ultrasonic. Cats hear even higher, up to about 85 kHz.

Traditional landline phone calls sample voice at 8 kHz, which by Nyquist captures frequencies up to 4 kHz. Human speech intelligibility lives mostly between 300 Hz and 3,400 Hz, so 8 kHz is just enough. It is why phone calls sound muffled compared to in-person conversation — you lose all the higher harmonics that make a voice sound natural. HD Voice (VoLTE) bumps the rate to 16 kHz, doubling the bandwidth and noticeably improving clarity.

IBM needed a clock that could derive both the CPU timing and the NTSC color-burst frequency (3.579545 MHz) for the built-in composite video output. Multiplying the color-burst frequency by 4/3 gave 4.77 MHz — a convenient compromise that let one crystal oscillator serve two purposes. The weird number was pure engineering pragmatism, not performance targeting.

The 433.05–434.79 MHz range is an ISM (Industrial, Scientific, Medical) band that is license-free in most of Europe. Cheap remote-control key fobs, weather stations, garage door openers, and IoT sensors all crowd into it because you can legally transmit at low power without a radio license. In the US, the equivalent unlicensed band is 315 MHz, which is why European and American car key fobs are not interchangeable.

AM encodes audio by varying the wave's amplitude, which is vulnerable to electrical interference (lightning, motors). FM varies the frequency instead, making it inherently noise-resistant. FM also has a wider channel bandwidth (200 kHz vs. AM's 10 kHz), allowing it to carry the full 20–15,000 Hz audio spectrum in stereo. The MHz carrier frequency itself isn't what improves quality — it's the modulation method and bandwidth.

Intel and AMD marketed processors by clock speed — 500 MHz, 1 GHz, 2 GHz — implying faster was always better. By 2004, Intel's Pentium 4 hit 3.8 GHz but ran so hot and consumed so much power that performance-per-watt cratered. The industry pivoted to multi-core designs: instead of one core at 4 GHz, you got two or four cores at 2 GHz each, doing more total work with less heat. Raw megahertz stopped being a useful buying metric.

Bluetooth operates in the 2.4 GHz ISM band (2,400–2,483.5 MHz), which is reserved globally for unlicensed use. This avoids the need for regulatory approval in each country. The trade-off is sharing the band with Wi-Fi, microwaves, and baby monitors. Bluetooth mitigates interference by hopping between 79 channels 1,600 times per second — if one frequency is jammed, it has already moved on.