It depends on the suppressor, but generally, they make handguns about as loud as a rock band and rifles about as loud as a jackhammer. The level of reduction will also depend on the caliber of ammunition being used. For example, a .22lr suppressor will provide much more noise reduction than a 9mm suppressor.
Suppressors can cut the noise of a gunshot by 30 to 40 decibels, which is about the same as earplugs or foam earmuffs. So, on average, a suppressor would make a gun sound like it is firing at around 130 to 140 decibels.
That being said, there is no definitive answer to this question because suppressors can vary in terms of how effective they are at muffling sound. The type of ammo you are using and the distance between the shooter and the target will also affect how loud gunshots sound.
In general, however, using a suppressor will significantly reduce the noise of a gunshot and make it much more tolerable for both the shooter and those around them.
A suppressed gun is much quieter than an unsuppressed gun. Suppressors reduce the noise of a gunshot by around 30 dB, which is about the same as earplugs. This is why many people use suppressors for hunting – it helps to avoid scaring away prey and also keeps the hunter from being heard by potential targets. It should be noted that suppressors do not eliminate the noise of a gunshot, so they should not be relied upon for stealth operations.