Fearful Harmony is the name given to a type of start-up error encountered on PlayStation 1 consoles, displayed when the system BIOS is corrupted due to the reading of non-PlayStation data as machine code. This causes the system to hang while displaying audio and visual glitches, caused by a combination of invalid instructions and reduced system performance. This error is triggered whenever the user inserts a damaged or non-PlayStation disk into a console modchipped to bypass copy-protection. It can also be triggered on an unmodded console by disk-swapping. This error only occurs on SCPH-100x and SCPH-5xxx models; models SCPH-7xxx and newer will return a Red Screen of Death. Fearful Harmony is part of a group of related errors (see Personified Fear, Forbidden Image, Callous Venture, Dreadful Harmony).
On startup, the Sony Computer Entertainment logo will appear as normal, however, as the console reads the invalid disk, the screen will stay on the Sony logo for longer than usual, until the screen changes to black with the PlayStation logo missing and the other visual elements staying on the screen, often glitched with parts missing. The 'PlayStation' text also fades in much slower than usual. The 'woosh' sound normally heard on this screen will be much louder. After 60 seconds or less, a slowed down version of the startup chimes will play for a while before more chimes begin to play at faster and slower speeds, as the console would attempt to read the disc. Eventually, the music will stop, and the console will freeze upon attempting to execute the loaded 'game data' all at once.
The cause of Fearful Harmony is due to a malfunction in the PS1's startup sequence. When the console is powered on, the BIOS is copied from ROM to RAM, and the loaded disk is checked for a digital signature known as an ATIP groove. This is to ensure the disk is authentic, and if a valid groove is detected, the data from the disk is written to RAM as normal and the PS1 logo displays. If this copy-protection is defeated by a modchip or via disk-swapping, the console reads the disk as if it were genuine. As a damaged or non-PS1 disk is read, the console interprets the data as erroneous machine instructions on how much data to read and where to write it. This will eventually overwrite the BIOS, causing the Fearful Harmony state. Unlike Personified Fear, the BIOS is only partially corrupted, enough to allow runtime to continue.
The most memorable feature of Fearful Harmony, the music, is a consequence of how the PS1's startup music is stored as sound data and played back. Unlike a discrete MP3 or WAV file, the PS1's startup music is played live with a MIDI controller which draws from three music samples in the BIOS to build its soundfont: a chime, glass breaking in reverse, and a synth wave from a Roland D-50. Like how playing MIDI samples on a lower or higher key affects the pitch-scaling and playback speed, these samples are likewise manipulated to create a whole piece of music from three basic 'instruments'. Different sections of the song are intended to play when the disk is read and verified, which is why the breaking glass 'woosh' sound always plays when the PS1 logo is displayed. In a state of Fearful Harmony, the MIDI controller begins replaying the chimes section of the PS1 startup music at a much lower pitch and slower speed. The music plays out while the console finishes reading and writing the disk, and the system freezes after both are completed.
Video glitches are caused by a lack of system memory and corrupted display instructions. The visual sequence involved in the PS1's startup sequence involves drawing assets to the screen and removing them when unneeded. This not only involves bitmap images but also 3D models as seen with the Sony and PS1 logos. What happens is that the polygonal data for the Sony logo which carries into the post-authentication screen is altered, leading to it taking on strange shapes. How the visual glitches appear depends on the disc you've inserted and the version of your console. Some show or hide the diamond, others make the 'PlayStation' text appear and disappear, and some graphics may be overwritten with others stored in the BIOS. Rarely, the screen will fill with pixels of random color creating a 'rainbow' effect, possibly due to the console mistaking dynamic RAM (DRAM) for video RAM (VRAM).
The reason why the PS1 logo is never present during Fearful Harmony is because the model is intended to be read from the game disk, which is missing on an invalid disk. This is similar to the Nintendo logo that displays at the beginning of every Game Boy game, which was required in every cartridge's ROM as copy-protection.