Two of Britain's leading film composers warn that the quality of music for film and TV is suffering because synthesised sounds are increasingly replacing real instruments in an effort to cut costs.

Carl Davis, whose scores include that for the World at War documentary series, said a synthesised soundtrack lacked "the heart" of symphonic or instrumental music.

Christopher Gunning, who wrote the Bafta-winning score for La Vie en Rose, about Edith Piaf, was even more critical: "A lot of television music has got to the stage where I have to turn it off. There's an enormous amount of programmes where I find the programme content really quite interesting, but can't watch because I find the music so blooming irritating. Part of that is, I am afraid, the poor quality of the musical composition. But part of it is also the sheer sound of it."

Davis acknowledged that some composers – such as Giorgio Moroder (Midnight Express), Maurice Jarre (Witness) and Vangelis (Chariots of Fire) – had proved the technology could work creatively. The problem with some synthesised sound lay in its lack of expression, he said: "I'm particularly impressed and appalled that you can write something, using it like a musical typewriter, and it will then play it back to you. But you're not playing it. One always has to take that into account, that distance from the actual production of the sound. That gives it a slightly dehumanised quality."

Davis's scores include The French Lieutenant's Woman and the BBC's Pride and Prejudice, as well as silent movies such as Buster Keaton's 1926 masterpiece The General, which will be re-released in cinemas from 24 January in a restored version, opening at the BFI Southbank in London.

Davis is concerned that the sheer proliferation of television channels is taking its toll on budgets for musicianship. Synthesised performances were "infinitely cheaper" than hiring an orchestra, he said: "You want more programmes, but there's less money to make them."

He would rather have "a single cello than something that sounds enormous but which you know is artificial".

Gunning said: "I have also done some scores using electronics on their own, but it's normally because there've been some financial constraints. Increasingly I hear of composers who are being forced to write and record the music in their bedroom, as it were, because there is simply no budget for live musicians." He had even heard of one composer being told: "Do this for nothing or not at all and we'll find somebody who will."

For that reason, he turns down TV commissions: "I haven't been offered anything with a proper budget."

In contrast, when he wrote the music for Dennis Potter's Cold Lazarus in the 90s, he was allowed eight sessions with a leading orchestra. "I don't think that would ever happen nowadays."

He dismissed synthesised sounds as a "bundle of notes", adding: "You just do not get the effect of a real live musician playing real phrases. It's quite extraordinary how a live musician can inflect a certain note with emotion."

Davis added that his experience of directors and producers had ranged from those who were musical and "very attuned to how effective the score is" to those who were "quite indifferent" to it. "I always say that, working in films, a composer can have no ego."

David Whelton, the Philharmonia Orchestra's managing director, expressed sympathy for the criticisms of synthesised sound, observing that "noticeably" fewer films were being scored for symphony orchestra than 20 years ago. Yet he added: "Music is one of the most powerful elements in making a film a success. In my experience, everybody would always jump at the chance to use a big symphony orchestra for a film score. It is only budget."

Referring to scores such as Jaws, whose music by John Williams conveyed the underwater menace so brilliantly, he said: "That's an absolutely great score. You can't get the score out of your mind. Every time you see the image, the soundtrack comes back, and every time you hear the soundtrack, the image comes back. That is a perfect partnership."

But Jeff Rona, a Hollywood composer whose synthesised soundtracks include Phantom, starring Ed Harris, said: "People were incredibly moved by the Oscar-winning – and all-electronic – score to Chariots of Fire, or the synthesiser-based soundtrack to Rain Man. Those synthesiser scores are both indelibly emotional.

"Economics has definitely led to the use of electronic instruments in films or TV that would have otherwise benefited from a more orchestral approach. But more often than not very few people even notice whether a soundtrack is orchestral or synthesised. We've simply become so used to it."

He argued that improved technology had made synthesised scoring more expressive and emotional. But he admitted that, for those who paid close attention to the soundtrack, there was nothing like the sound of a real orchestra for sheer power and emotion.