MARK Smith blames the curse of mumbling in TV drama on an acting fad which has got out of hand (“The real reason there is mumbling on TV”, The Herald, February 24). True, but not the whole story.

A fundamental of broadcasting, once axiomatic, now largely forgotten, is that sound is more important than image. Imagine a low-budget, hand-held documentary shot in low ambient light. Let’s assume the subject matter is compelling. If the exposure is dodgy and the camera operation erratic but the digital sound clear, the viewer can and generally will stay with it; if it’s the other way round – superb imagery but muddy sound - most viewers will turn off.

Why? Because the eye is an infinitely adaptive, patient detective, continuously inferring, intuiting, and interpreting. But where relevant sound (chiefly human speech) is unintelligible, the cause is lost. The viewer gets one chance to hear and understand before the narrative moves on. Language, what makes us human, the words we say to one another, the thoughts we share, are more important than the surface of things. (Industry jargon is telling: good sound is often referred to as “bright”.) But we live today in the age of the image.

Mr Smith is right that mumbling is in fashion. That revolution started with Brando. He began in the discipline of stage technique, where the theatregoer in the back row must hear his softest whisper; but in the cult of the modern cinema star many of the prayers are mumbled, all in the cause of realism. Brando had the chops to slur words clearly and with élan, but many of his imitators today simply lack technique.

The soundtrack is also coarsened by the ubiquity of music – or more often muzak. This can plague drama but increasingly it’s the bane of almost every genre. It’s all over daytime telly and even the flashier evening offerings. It is moronic, and there’s usually one reason for it: producers fear that their product is too banal to be of interest as it stands. They think muzak contracts the time sense for the viewer, who is believed to have a short attention span. The metric is obvious: the more muzak, the greater the insecurity of the producer or director. They worry they are pumping out rubbish, and ninety-five per cent of the time they are.

Martin Ketterer,

Sandringham Court,

Newton Mearns, Glasgow.