I am interested in different timescales of change in audio systems.
I believe that all changes to all parts of the sound-producing system have the potential to change the sound.
The sound-producing system includes the hifi components, the room, the air in the room, the listener, the electrical environment, what surrounds the room, etc.
Some changes are not great enough to register as changes to the listener, and are therefore not audible.
Whenever the listener perceives a change of sound quality, there will be an infinite number of changes to the system (if you include all possible scales of size of parts of the system).
Interesting questions concern which of the changes were responsible for any actual changes in the sound that a microphone might pick up - and which changes were mainly changes to the hearing system and mind/brain of the listener?
What is also of interest is the idea that an excellent home hifi system will change every day sometimes more and sometimes less.
So there is a significant range in the daily, weekly and monthly amount of change, owing to change in the rate of change of things like:
- quality of hifi components and media, and how they work together
- temperature and pressure
- EM noise
- background noise (soundwaves)
- seismic activity and vibration and movement in and through the room
- drying out of caps and other thermodynamic changes (entropic and negentropic) to the system
- mood and concentration of the listener
- whether the listener enjoys that music at that time
- presence of others in or near the room
- hearing ability of the listener
- changing ability of the listener to tune into different aspects of sound due to musical education (or stagnation) - inc. changes in understanding of musical instruments, composers, musicians, etc.
Given all this it is no wonder that it can be hard to remember all aspects of the sound quality of the sample of music (e.g. PRaT, timbre, tonality, volume, harshness, balance, etc.) and compare it to another one.
It’s also not surprising that people find it hard to discern the effect on SQ of changes to one component over days and weeks - as all components are changing in some ways all the time.