Clash

Clash is a peak distortion caused by over modulation of the light valve of an optical recorder. The light valve opens and closes to expose light onto an optical sound track negative, photographing audio in the form of a sound wave. The louder the sound, the wider the light valve opens, exposing more light onto the negative. Volume levels that are too high have too much low frequency information, too much high frequency information, or any combination thereof can cause the light valve to be over modulated and eventually collide, or “clash,” together.

During over modulation, the optical recorder's light valve is held wide open and then completely closes for too long because it cannot react fast enough to the high levels being sent to it. Over modulation can occur if an optical sound track negative is made from a source that has been print mastered improperly – or not at all – prior to recording. The valve collisions during over modulation create gaps in the photographed sound wave that in turn cause the clipping type of peak distortion when played back. This peak distortion can sometimes be corrected by printing if it is not too severe. However, if the clipping is prolonged then it can't be fixed by printing, as intermodulation (IM) distortion will result. Neither printing nor filtering can fix IM distortion.

To avoid clash, all tracks intended for optical recording should be print mastered.

In this clip, the clashing occurs during the gunshots, which sound distorted and lack definition.

Playback using algorithms of Chace Audio's COSP-Xi technology has reduced the effect of the clash recorded to the film; the gunshots now sound more realistic and less distorted.

When an optical recorder's light valve is held open, too much light gets through; this will cause the thick black sections in this image of a clashed negative. When the valve is held closed, no light gets through, causing the gaps seen here in between the black sections. This sort of wave form will be sound clipped upon ordinary playback.

For comparison, here is an image of a dual bilateral negative that does not display the gaps track caused by clashing.