Complaints to the BBC about inaudible dialogue in Jamaica Inn have risen to nearly 800 following last night's second episode.

The BBC said it would turn up the volume on the drama, starring Downton Abbey actor Jessica Brown Findlay in the lead role, after viewers took to Twitter to complain about Monday night's opening instalment.

But its efforts to solve the problem did not stop the flow of complaints.

A further 429 people complained in advance of Tuesday's second episode, with another 252 complaints received after its transmission at 9pm last night, a total of 798 complaints by Wednesday morning.

The sound difficulties may also have hit the BBC1 drama's audience, which saw its ratings plummet a quarter to 4.5 million last night, down from 6.1 million the night before.

Although it is not unusual for a drama to lose viewers during the course of its run, a fall of 1.6 million viewers may be regarded as precipitous.

Emma Frost, who adapted the Daphne du Maurier novel, said there was a "major sound problem" with the opening broadcast.

The dialogue of Joss Merlyn, the landlord of the Jamaica Inn played by Sean Harris, proved particularly problematic.

Frost told her Twitter followers to "spare a thought" for one of the drama's sound operators, Matt Gill. "Be nice to him. He's crying," she said.

Gill tweeted: "Do I dare watch episode 2?" He added: "Got some texts from the rest of my sound team just as confused as me … Unfortunately we're all working night shoots on different jobs so none of us actually saw the transmission."

"How does budget affect technical broadcast issues? Piece of advice, after production, budget has nothing to do with broadcast," said Gill.

"I don't think anyone 'let' it go out like that. Technical faults happen … Best guess is a transmission problem as it sounds fine on previews, episode two broadcast and iPlayer."

The complaints came almost a year after BBC director general Tony Hall said the corporation could look at how to stop actors "muttering" in its TV dramas.

The concluding episode of the three-part drama will air on BBC1 on Wednesday night.

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