The One Network, including London's Capital 95.8 and Birmingham's BRMB, has seen its overall reach decline owing to BBC Radios 1 and 2.
It plans to introduce more content to run simultaneously on all stations, and new jingles to create a consistent style and tone. GCap has outsourced jingle production at a cost of £250,000, and chosen Music4 to produce the content.
New shows will run on weekend mornings, and there will be more celebrity news. The station websites will also provide more local information.
The One Network's reach for the second quarter of 2007 was 7.2 million, down from 7.4 million for the same period in 2006. Its audience share was also down from 10.2 per cent to 9.8 per cent.
Mark Lee, GCap's managing director, regions, said: "This is about strengthening the stations' national proposition, while shifting the local proposition towards personalised information."