Sound is what sets off the best memories—ahead of sight and even smell, according to a new poll.

Birds singing and waves crashing on the shore were among the top sounds most likely to trigger people's fond memories.

A study of 2,000 adults, aged 50 and over, found four in 10 people experience sounds that prompt nostalgic thoughts a couple of times a week.

For some, rain on the windows, sheep bleating, and a train going down the tracks are enough to make them smile.

Other respondents said these sounds transport them to another place in another time, including trees blowing in the wind, a crackling fireplace, and church bells.

Gordon Harrison, chief audiologist at Specsavers, which commissioned the survey, said, "Sound impacts most aspects of our lives, so it is no surprise that certain sounds trigger happy youthful memories."

This is particularly true when it comes to sounds of the outdoors. These trigger memories of good times for 67 percent of adults. No wonder 78 percent of those polled said they tend to spend lots of time outside.

And of the 94 percent who have access to their own outdoor space, they'll spend an average of five hours in it every week – with 72 percent referring to it as their ‘happy place'.

The kettle whistling, the radio playing, and cats purring also featured in the top 40 positively-triggering sounds, according to the over 50s. More than three quarters said that as they grow older, they treasure their happy memories more.

However, more than half of respondents admitted their hearing has deteriorated with age, yet only 26 percent have had it checked by an audiologist.

A full 90% confessed they took their hearing for granted in their younger years, according to the survey, carried out through OnePoll. And 45% worry about their hearing getting worse, especially when being questioned about losing the ability to have some of these pleasurable memories triggered by the sounds around them.

TOP 40 MEMORY-TRIGGERING SOUNDS FOR THESE OVER 50s:

1. A specific song or piece of music 2. Waves crashing on the shore 3. Birdsong 4. A crackling fireplace 5. Walking on fresh snow 6. A waterfall 7. Cat purring 8. Trees blowing in the wind 9. Rain on the window pane 10. Rustling leaves 11. Church bells 12. Bees buzzing 13. A thunderstorm 14. Rain patter on leaves 15. Children playing outside 16. Lawns being mown 17. A fountain 18. The radio playing 19. Sheep baaing 20. Seagulls squawking 21. A train going over tracks 22. Cows mooing 23. A cork popping 24. Dinner being served up 25. Pouring a drink 26. Mail being delivered 27. Food cooking on the hob 28. Cicadas humming 29. Sports stadium/arena 30. The kettle boiling 31. An airplane flying overhead 32. A crowd cheering 33. Horses galloping 34. A beer bottle/tin being opened 35. Dog barking 36. Fish jumping out of water 37. Street entertainers 38. A toaster popping 39. A coffee grinder 40. A garden sprinkler

Do you have a different sound that puts you in your happy place?