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Changing the Macintosh Start-Up Sound

Beep! Wouldn’t it be fun to customize the cheery little square wave greeting of your Mac 512K or Plus? With a Macintosh ROM-inator kit installed, now you can. This isn’t a control panel like SoundMaster, that plays while the OS is loaded from disk – it’s the sound that you hear the moment you flip on the power switch. On a normal vintage Macintosh, this sound is generated on the fly by code in ROM, but with ROM-inator you can alter this behavior and create any kind of sound you’d like. Let’s get started!

This tutorial assumes you already have a ROM-inator kit installed in your Mac 512K, 512Ke, or Plus. If not, follow the link to learn more or buy a kit. The ROM-inator is capable of many customizations beyond just startup sound hacks, including making a bootable disk contained entirely in ROM.

The steps below may look long and complex, but that’s because I want to be thorough and avoid skipping any details. In a nutshell, all that’s necessary is to convert a sound to the proper format, optionally patch a byte in ROM to reflect the sound’s duration, and then use Flash Tool to store the new sound in ROM.

Making the Start-Up Sound

First, you’ll need a sound sample to replace the default beep. This can be something you recorded yourself, or a sound downloaded from a source like The ideal sound will be 0.66 seconds in duration, matching the length of the standard beep sound, but durations from 0 to 1.3 seconds are possible if you’re willing to do a small amount of extra hacking as explained below. For this exercise, I’m going to use the MOOF! sound of Clarus, the DogCow, which I found here. The DogCow was the mascot of Apple Developer Technical Support for many years during the vintage Macintosh era.

Next, you’ll need to convert your sound to mono 22 kHz 8-bit unsigned raw format. The free audio tool Audacity can do this, converting from other formats like WAV or MP3 if necessary. The “moof” sound is a WAV file, so let’s open it with Audacity and take a look:


The moof sound is just under 1.5 seconds in duration – longer than the 1.3 second limit. Fortunately everything from about 1.2 seconds onward is just silence, and can be deleted. In the Audacity window, click the mouse in the timeline at 1.2 seconds, then drag it to the right to select the range from 1.2 seconds onward. Then hit the delete key on your keyboard, and everything from the 1.2 second mark to the end will be removed. In my case, I ended up with a sound that Audacity said was 1.203 seconds in duration.

The screenshot shows that the moof sound is mono 8 kHz 32-bit float format, so it needs to be converted. First, change the “project rate” selection in the lower-left corner to 22050. Then go to the File menu, and select “Export…”. In the dialog box that appears, press the Options button, and select RAW (header-less), Unsigned 8 bit PCM. The “Save As Type” should be set to “other uncompressed files”. Then save the converted file. If a box appears asking for metadata, ignore it and save. See screenshots:



Adjusting for Sound Duration

If your sound is 0.66 seconds long, then you’re done – you can move on to the next step below, storing your new sound in ROM. But if the sound is longer or shorter than 0.66 seconds, you’ll need to make a one-byte change to the Mac ROM startup sound routine. If you don’t make this change, your sound will either be cut off too early, or will keep playing past its end while interpreting random memory as sound data. It won’t hurt anything, but it won’t be very pleasant for your ears.

Download the file code-patched.bin, which contains the default ROM code for ROM-inator. (By the time you read this, the version linked here may be out of date – see the ROM-inator main page for the latest version.) You’ll need a binary editing tool such as xvi32 to make a one-byte change to this file. Open the file, and examine the byte at offset 0xEF hex, which is offset 239 in decimal. The value at that offset should be 0x28 hex, or 40 decimal. This is the duration of the startup sound, in sixtieths of a second.


Multiply the duration of your sound by 60, truncate the result to a whole number, and write it at offset 0xEF, replacing the 0x28 value that was there previously. My sound is 1.203 seconds, times 60 is 72.18, so I’ll write the value 72 decimal, which is 0x48 hex. Then save the modified file as code-patched-for-sound.bin.

Storing the New Sound

The last step is to copy the files you created onto your vintage Mac. You’ll need to copy the new sound file, the duration-adjusted ROM code (if any), and the utility program Flash Tool (found on the ROM-inator page). My preferred way to copy the files from a modern PC to a Mac Plus is with Floppy Emu, but it can also be done via a Localtalk network, or by using another Macintosh as a bridge machine for copying to an 800K floppy disk. With Floppy Emu, I put a blank 800K disk image file on my SD card, use a tool like HFVExplorer (Windows) or Fuse HFS (Mac OS X) to copy the files into the blank disk image, then put the SD card in the Floppy Emu and connect it to the vintage Mac.


Run Flash Tool on the Mac, and click the radio button to indicate you want to update ROM with a new startup sound. Select the sound file you made, and hit the “Update ROM” button to perform the update. The process only takes a few seconds. If your sound’s duration was not 0.66 seconds and you made a duration-adjusted ROM code file, you’ll need to store that in ROM too. Click the radio button to indicate you’re performing a ROM code update, select your code-patched-for-sound.bin file, and apply the update.

Happy sound hacking!

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1 Comment so far

  1. MJ April 14th, 2015 5:22 pm

    LOL! I changed the startup sound to a turkey gobble. Why? Well, because I can. Directions were great. 🙂

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