Chime

The startup chime used in Mac computers indicates that the Mac successfully passed the diagnostic tests at startup.

Enabling/disabling the startup chime

macOS Catalina or older

To disable the chime, type in the following Terminal command: sudo nvram SystemAudioVolume=%80
To enable the chime, type in the following Terminal command: sudo nvram -d SystemAudioVolume

macOS Big Sur or newer

Choose Apple Menu -> System Preferences..., then click Sound. In the Sound Effects pane, use the “Play sound on startup” setting to turn the startup sound on or off.

Extracting the chimes

Regular Intel Macs

The startup (and attach) chimes are located in the UEFI firmware. To extract it, use UEFITool. Then, search for the BootChimeAudio section. Finally, extract the Raw Section inside it by right clicking on it, and selecting Extract body.... Since it is a CoreAudio file, make sure to add the .caf extension on the file. The similar method applies to the attach chimes, but the section has no codename on it. To easily look for the chimes, after opening the UEFI firmware in UEFITool, select Action -> Search.... From here select Text and search for caff. Make sure to disable the Unicode option.
On T2 Macs, the UEFI Firmware contains the older 1998 chime. The chimes are CoreAudio (CAF) files with the following attributes: 16-bit, Mono at 44100 Hz with the IMA QT ADPCM Audio (ima4) codec.

T2 Macs

On T2 Macs, the chime is located in bridgeOS in /System/Library/PrivateFrameworks/BridgeAccessibilitySupport.framework/AXEFIAudio_VoiceOver_Boot.aiff. While it has the .aiff extension the chime is actually encoded in the Apple Lossless Audio Codec (ALAC) in a CoreAudio (.caf) container. The attributes are: 16-bit, Stereo at 48000 Hz with ALAC.
On Macs with bridgeOS 4.6 or earlier, the boot chime file name is the same, but the file is in an Audio Interchange File Format (AIFF) container and the attributes are different: 16-bit, Mono at 24000 Hz in the IMA QT ADPCM Audio (ima4) codec.
The charging chime is stored in /System/Library/Audio/Sounds/connect_power.aif. It is in an AIFF container with the following attributes: 16-bit, Stereo at 44100 Hz in the twos codec.

Apple Silicon Macs

Apple Silicon Macs use raw audio files to play the startup/charging chime. They are located in the macOS IPSW in Firmware/embeddedaudioresources/image4. To extract them, first extract the img4 header, and from here, open Audacity, click File -> Import -> Raw data and specify the parameters. To export, click File -> Export -> Export as WAV/MP3/OGG/other. Some devices use the same chime despite being put into separate files.
The parameters:

• (j274/j375c/j375d)-boot-chime.im4p: 32 bit PCM, Mono at 24000 Hz.
• (j293/j413/j493)-(attach/boot)-chime.im4p: 32 bit PCM, Stereo at 48000 Hz.
• (j313)-(attach/boot)-chime.im4p: 32 bit PCM, Stereo at 24000 Hz.
• (j456/j457)-boot-chime.im4p: 32 bit PCM, Mono at 96000 Hz.
• (j314c/j314s/j316c/j316s)-(attach/boot)-chime.im4p: 32 bit PCM, 6 channels at 24000 Hz.