Stump Microphone and Snickometer Explained: How Sound Technology Detects Edges in Cricket

Two technologies help determine caught-behind dismissals in international cricket: the stump microphone (an audio microphone embedded in the stumps that captures sound near the ball's path) and Snickometer (or UltraEdge — a graphical spike visualisation of the stump mic audio, showing when sound is detected near ball-bat proximity). Together, these tools allow TV umpires to detect tiny edges that are invisible to field umpires and sometimes to the batsman themselves. They are part of the Decision Review System (DRS) — used when a team challenges a caught-behind or LBW decision.

How Snickometer and UltraEdge Work

The technology behind sound-based edge detection: (1) Stump microphone: a microphone embedded in or near the stumps captures ambient sound during delivery. The stump mic audio is processed and synced to the broadcast frame-by-frame; (2) Snickometer (original): developed by Allan Plaskett in 1996, the Snickometer shows an audio spike graph — a visual representation of sound levels over time. A spike in the audio corresponding precisely to the moment the ball passes the bat indicates contact (an edge). The graph is overlaid on the ball-trajectory replay; (3) UltraEdge: developed by Hawk-Eye (the ball-tracking company) and introduced in 2013, UltraEdge is the more sophisticated evolution of Snickometer. It shows the audio waveform alongside the video frame — the analyst can see whether the audio spike occurs when the ball is in proximity to the bat or when it hits the pad (which would not be an edge). UltraEdge also uses multiple microphones for triangulation; (4) The limitation: stump microphones pick up all sounds — bat on pad, bat on glove, bat on ground, pad on ground — not only bat-on-ball edges. Analysts must determine whether the detected sound corresponds to ball-bat contact or one of these non-edge contact points. The proximity of the spike to ball-bat location (in the video replay) is the primary disambiguation tool.

Hot Spot: The Complementary Technology

Hot Spot is a thermal imaging system used alongside Snickometer/UltraEdge for caught-behind reviews: (1) How it works: Hot Spot cameras (infrared) capture heat generated by friction — specifically, the minute heat signature produced when the ball contacts the bat or pad surface. A small white mark visible in the infrared image at the ball-contact point indicates contact; (2) Limitations: Hot Spot does not detect all contacts. Very fine outer edges (ball barely touching the outer rim of the bat) may not generate enough friction to produce a visible Hot Spot mark. Wet conditions (rain, sweat) can produce false positive heat signatures. Wooden bats treated with certain oils may also show false negatives; (3) Hot Spot vs UltraEdge: Hot Spot has been removed from some DRS implementations (several bilateral series, particularly those involving teams not willing to pay for Hot Spot's licensing cost). UltraEdge/stump mic audio is more universally available because microphones are cheaper and already embedded in most broadcast setups; (4) The combination: when both technologies agree (Hot Spot shows a mark AND UltraEdge shows an audio spike at the same moment), the evidence for an edge is compelling. When they disagree (Hot Spot shows no mark but UltraEdge shows an audio spike), the umpire's call and the Umpire's Call principle in DRS may apply.

Why Some Decisions Remain Controversial Despite Technology

Technology limitations that create ongoing controversy: (1) Glove vs bat: when the ball hits the batsman's glove (which holds the bat handle), UltraEdge will show an audio spike. But a hit on the glove is a caught-behind dismissal only if the glove is touching the bat at the time. If the glove is not touching the bat (e.g., if the batsman's hand is slightly separated from the handle), it is NOT a caught-behind dismissal. Determining whether the spike came from the bat or the glove alone requires the thermal Hot Spot to show where the heat trace is — another reason why Hot Spot and UltraEdge work best together; (2) Soil/debris: foreign material on the bat surface can create unexpected sounds. A ball hitting debris on the ground near the bat creates an audio spike that is not a dismissal; (3) The edge-and-pad sequence: sometimes the ball edges the bat first and then hits the pad — both a caught-behind and an LBW dismissal are possible in the same delivery. The fielding team must decide which to appeal. If they appeal caught-behind and the umpire gives not out (the umpire did not hear the edge), a DRS review with UltraEdge can show the edge. If they then find LBW was also plausible (ball hitting stumps in ball-tracking), the result depends on which was the first contact.