The original version of SoundMeter, which was available in the App Store soon after its opening in 2008, has been replaced by new subscription-based and perpetual license apps. If you purchased the legacy version of SoundMeter, you may continue to use it. If you need to re-download it, you may do so for free. Please visit Apple's support site for instructions on how to re-download previously-purchased apps:
Subscriptions: Continuous Access to the Latest Tools and Features, Free to Try
You can download SoundMeter X for free. Standard SoundMeter functionality, including the Sound Level Meter and Noise Dosimeter, is free to use indefinitely. For access to more powerful tools and additional features, a subscription is required. You can try a subscription for free for up to 7 days.
Professional mobile sound level meter.
Perpetual License: Pay Once, Use Indefinitely
SoundMeter Pro 2020 will continue to receive maintenance updates through 2021, after which it will continue to work indefinitely on compatible versions of iOS (iOS 10 through the latest iOS at the end of 2021).