Bandwidth

Audio

Bandwidth has two distinct meanings in AV systems, both in common use:

  1. Analog/acoustic bandwidth - the range of frequencies a signal, device, or channel can carry; measured in Hz
  2. Network/digital bandwidth - the maximum data rate of a digital communication link or channel; measured in bits per second (bit/s) or multiples thereof (Mbit/s, Gbit/s)

The two usages are related - higher analog bandwidth in a digital system requires more network bandwidth to represent it - but the terms refer to different physical quantities and should not be used interchangeably.

Analog Bandwidth

In analog audio and video, bandwidth refers to the span of frequencies a device or signal path can handle. It is typically defined as the range of frequencies over which a device’s response remains within a specified tolerance (commonly ±3 dB).

Audio Bandwidth

Human hearing spans approximately 20 Hz to 20,000 Hz (20 kHz). Professional audio equipment is typically specified to be flat (±0.5 dB or better) across this range. The usable audio bandwidth of various systems:

SystemBandwidth
POTS telephone300 Hz - 3.4 kHz
AM radio~100 Hz - 4 kHz (audio bandwidth)
FM radio20 Hz - 15 kHz
CD audio20 Hz - 20 kHz (44.1 kHz sample rate → Nyquist limit 22.05 kHz)
Professional audio (96 kHz)20 Hz - 48 kHz (above hearing)

Video Bandwidth

In analog video, bandwidth determines the horizontal resolution: the higher the bandwidth, the finer the detail the signal can carry. Standard definition NTSC video has a video bandwidth of approximately 4.2 MHz. High-definition analog component video (HDTV) required up to 30 MHz per channel, which drove the shift to digital distribution.

Digital / Network Bandwidth

In networking and digital AV, bandwidth refers to the maximum data throughput of a link or interface. This usage comes from information theory: Shannon’s theorem (1948) showed that the maximum information rate of a channel is proportional to its analog bandwidth - hence the borrowed term.1

Interface Bandwidth Reference

InterfaceMax bandwidth
Fast Ethernet (100BASE-TX)100 Mbit/s
Gigabit Ethernet1,000 Mbit/s (1 Gbit/s)
10G Ethernet10 Gbit/s
USB 2.0480 Mbit/s
HDMI 1.410.2 Gbit/s
HDMI 2.018 Gbit/s
HDMI 2.148 Gbit/s
DisplayPort 2.1 (UHBR20)80 Gbit/s
SDI (3G-SDI)2.97 Gbit/s
SDI (12G-SDI)11.88 Gbit/s

Why Bandwidth Matters in AV Design

  • 4K at 60 Hz with 4:4:4 color requires approximately 12 Gbit/s of raw video data - requiring HDMI 2.0 (18 Gbit/s) or DisplayPort 1.4 (32.4 Gbit/s).2 HDMI 1.4 (10.2 Gbit/s) can only carry 4K at 30 Hz, or requires chroma subsampling to 4:2:0 at 60 Hz.
  • AV over IP streams audio and video as compressed data over Ethernet. Uncompressed 4K at 60 Hz would require ~12 Gbit/s; H.265 compression reduces this to 20-50 Mbit/s for streaming or 1-3 Gbit/s for professional lossless distribution.
  • Bandwidth reservation in AVB/TSN networks (see Audio Video Bridging) allows audio streams to reserve a defined fraction of available Ethernet bandwidth, guaranteeing bounded latency.

History of the Term

The word “bandwidth” entered electrical engineering from radio communications, where it described the range of radio frequencies occupied by a transmitted signal. Early amplitude-modulated (AM) radio occupied a bandwidth of twice the highest audio frequency (a voice signal up to 4 kHz occupies an RF bandwidth of 8 kHz). The term was formalized in the Radio Regulations of the International Telecommunication Union (ITU) in the 1920s-1930s.3

Claude Shannon’s 1948 paper “A Mathematical Theory of Communication” gave bandwidth its precise mathematical relationship to information capacity (the Shannon-Hartley theorem), which is why the networking community borrowed the term for data rate from the 1960s onward.1

Footnotes

  1. Shannon, C.E. (July 1948). “A Mathematical Theory of Communication” (PDF). Bell System Technical Journal. 27 (3): 379-423. doi:10.1002/j.1538-7305.1948.tb01338.x. (Defines channel capacity as a function of bandwidth and signal-to-noise ratio.) ↩ ↩2

  2. HDMI Forum. HDMI Specification 2.0. 2013. (Defines 18 Gbit/s aggregate bandwidth; Table of supported video formats at 4K/60 Hz.) ↩

  3. International Telecommunication Union. “History of ITU”. ITU. (Background on ITU Radio Regulations development from 1906; bandwidth definitions formalized in international coordination agreements.) ↩

Related Terms

1/3 octave equalizer1/4-inch phone connector1/8-inch phone connector3.5mm phone connector6.35mm phone connector

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