Cable Impedance Calculator — Characteristic Impedance

Characteristic impedance (Z0) is the impedance that a cable presents to a signal travelling along it. It is determined by the cable's inductance and capacitance per unit length: Z0 = √(L/C). It is independent of cable length.

For digital audio (AES/EBU at 110Ω, S/PDIF at 75Ω) and video, impedance mismatches cause signal reflections that corrupt data. For analogue audio at low frequencies, impedance matching is less critical because wavelengths are much longer than cable lengths.

Only digital and coaxial cables are specified for a controlled characteristic impedance: AES3/AES-EBU balanced digital = 110Ω, and S/PDIF coaxial = 75Ω. Analogue microphone and instrument cables are NOT manufactured to a controlled Z0 — their characteristic impedance is frequency-dependent and almost never quoted on the datasheet, because at audio frequencies the wavelength is far longer than any normal cable run so reflections are negligible. Speaker cable is chosen for low series resistance (often well under 1Ω total), not for impedance. As a sanity check, a real AES/EBU cable such as the Belden 1800F (0.18 µH/ft ≈ 0.59 µH/m, 12 pF/ft ≈ 39 pF/m conductor-to-conductor, velocity of propagation 76%) is swept-tested to the 110Ω nominal.