Poor bass-less sound on HP EliteBook 2560p

Every once in a while the audio in my EliteBook 2560p (Windows 7) does not work properly:    Music on the headphones sounds as if it was being played through a high-pass filter, and at a low volume.    

I thought it was an issue with the fact that the audio jack is prepared for a headset (with microphone) and not really for regular headphones.  

But it turns out that the audio problem goes away some times, and music sounds just fine.

I rarely reboot this machine:  I either suspend it, or hibernate it.    It seems something goes wrong with the audio sometimes when sleeping/hibernating, but I never knew what it is.

Today I finally found a solution:   There is a Windows 7 service called "STacSV" ("Audio Service", described as "Manages audio jack configurations").    The service was stopped;   all I had to do is hit "Start", and the music on the headphones instantly began to sound correctly in full frequency range, with proper bass and volume.