It's not just that people aren't drinking soda -- they're not talking about it either.

According to a new report out from the Keller Fay Group, word of mouth impressions for Coke, Pepsi, Dr Pepper and a slew of other soft drinks have been steadily declining since 2011. Last year, Coke ceded its most-talked-about-brand status to Apple.

Since 2011, face-to-face conversations are down 6% at Coke and 9% at Pepsi. One bright spot in the soda category is Coca-Cola's Fanta brand, which saw word-of-mouth impressions increase 11%. And during the same time, social-media conversations are up 39% for Coke and 31% for Pepsi. But social-media conversation is rising off of a small base and is still a small part of the equation. In 2013, for example, face-to-face conversations accounted for 84% of word of mouth, while social media was 2%. The overall sentiment of conversations about soda, both online and offline, is positive.

Ed Keller, CEO of Keller Fay Group, said there's been a surge in conversations about brands like Apple, Samsung, Verizon and AT&T. "When it comes to cultural relevance, a lot of the technology brands are taking up people's talk time," Mr. Keller said. "It presents a challenge to the soft drink industry. It certainly suggests that the sales decline is likely to continue for carbonated soft drinks."

Consumers have been shunning soft drinks in favor of tea, energy drinks and bottled waters for years, but defected from the category at an even faster rate in 2013. Carbonated soft drink volume declined 3% in 2013, compared to a 1.2% decline in 2012 and a 1% decline in 2011, according to Beverage Digest. The category has seen declines for the last nine years.

It is worth noting that the number of word of mouth impressions for soft drinks exceeds that of alcoholic beverages, still beverages, sports drinks, energy drinks and coffee combined.

"The takeaway is to focus on the totality of conversation about your brand. That's what ultimately ties to sales," Mr. Keller said. "There's a need for carbonated soft drinks to do some investigating to see how to regain a foothold."