Recording sound volume

[dirkjently]

Does anyone know if there Is anything on the market that can measure sound volumes (in dB) over time?  

I inherited quite a nice old stereo amp/pre-amp system that my dad and a family friend built however recently i swear it is louder for the first 10 min of it turning on and then goes quieter once it has warmed up. 

 

I want to try and measure it but most things that I have found that can measure decibels only do it for a short period of time so its really hard to tell if the volume change is subjective based on what i'm listening to, if the volume is slowly changing as the system warms up or if something is overheating and limiting the output.  

 

I even thought I might need to build something, but most kits i have found look at recording the sound content not the volume in decibels and i don't know enough software wise to write a program to run on a raspberry pi or arduino and make sure that the recording device isn't sound leveling the recording.