Fearful Harmony is the name given to the startup error on the PlayStation 1 whenever the user inserts a non-PSX disc or a busted or pirated PS1 game to a modchipped console.
On startup, the Sony Logo will appear as normal, and then in most cases, it will attempt to boot up the improper disc in the PS1, as the user modchipped the console, however, it will play the second sound without the PlayStation logo. This sound is different to the normal PS1 bootup sound. The word 'Sony' will still be on the screen, and the orange-yellow diamond will still be there too. Well, at least half of it.
After about a minute or less, a (very) slowed down (0,5x speed) version of the startup chimes will play for a while, which was known to terrify children and would be unpleasant to adults. The chimes would intensify as the PS1 was trying to read the disc.
This error screen varies, depending on what disc you've inserted and what PS1 model you have. Some show the diamond, the acronym SCEA or SCEE, the word PlayStation appearing and disappearing, and strange glitched graphics.
During Fearful Harmony, the boot screen is advancing at a very slow pace due to the system trying to read and interpret invalid data off the disc. The chime sounds are being issued to play further apart, which also results in the looping of sounds for a much longer time. The Fearful Harmony ends once the system gives up (stuck at the boot screen without sound), or finishes scanning the data on disc.
Comparison from Forbidden Image
Most people are confusing the difference of this error. The forbidden image is only a short error, while the fearful harmony is a long error. The Forbidden Image displays only Sony, PlayStation and SCEA or SCEE, while the Fearful Harmony shows strange images. The second sound of the Forbidden Image is the same, while Fearful Harmony is different.
PSX Personified Fear
This, though less frightening, happens for the same reason with unreadable PSX games. The startup screen will show, followed by a black screen with a horrible sound. After the sound, the screen will stay dark, making users expect a nonexistent jumpscare.
The "horrible sound" mentioned above is reversed and pitched down glass shattering plus slowed down (0,25x speed) version of startup chimes. This sound is usually played and faded out when transitioning into the PS logo screen. When Personified Fear occurs, the system slows down as it's trying to read invalid data off the disc. The glass shatter sound is played, but doesn't fade out, and the chimes come in slowly and at low pitch.