What the research suggests about music
Several studies, including work done in shelter environments, have found that dogs exposed to slow-tempo classical music showed signs associated with lower stress, more resting behaviour, less vocalising, compared to no music or to more energetic genres like heavy metal or pop, which some studies associated with increased restlessness. The effect size in most of this research is modest rather than dramatic, and dogs, like people, likely respond somewhat differently to different music based on individual temperament.
It's worth noting that a lot of "calming dog music" playlists marketed specifically for pets haven't been independently tested the same way general classical music has, the safest bet based on current evidence is slow-tempo instrumental music generally, rather than a specific commercial product.
How white noise works differently
White noise or steady background sound (a fan, an air purifier, low TV volume) works through a different mechanism, it doesn't calm a dog directly so much as it masks sudden, sharp sounds that would otherwise startle them. This is particularly useful for dogs sensitive to unpredictable noises like fireworks, thunder, garbage trucks, or neighbours' doors, where the goal is reducing the chance of a jarring, sudden sound cutting through silence.
Where this helps most
Background sound tends to help most with situational, mild stress, settling at bedtime, reducing reactivity to street noise, or softening the edges of a stressful event like fireworks in the distance. It's also a reasonable low-effort addition for dogs left alone during the day, as part of reducing overall environmental unpredictability.
Where it falls short
For a dog with a diagnosable noise phobia, generalised anxiety, or separation-related distress that causes destructive behaviour or injury, calming music is a supporting tool at best, not a solution. Playing music during a genuine panic response won't override the fear response on its own; the underlying anxiety needs to be addressed through desensitization, counter-conditioning, environmental management, and in some cases veterinary input.
Building it into a routine
Music or white noise tends to work best as a consistent part of a dog's environment rather than something switched on only during a crisis, for example, playing during every nap time or bedtime so it becomes associated with rest generally, not just deployed reactively when your dog is already distressed. As with most calming aids, give it a few weeks of consistent use before deciding whether it's making a real difference, and combine it with training and management rather than expecting it to work in isolation.