DMX Files Frequently Asked Questions

Last update 2001-09-06

Q Can I tune the pitch of DMX sounds?
A Yes, all DMX voices have a pitch adjustment pot inside the case, on the voice card. Remove two screws on the lower front edge of the DMX case and raise the hinged lid to access the inside of the DMX. Look for the trim pots near the back of the case, on the top corner of each voice card.

Q How do I replace the battery in my DMX?
A Any 3.6 volt nicad battery of the same approximate physical size should work. Digi-Key ( part number P109-L031-ND is essentially identical to the factory stock part.
Be sure to disconnect all power and audio cables from your DMX before soldering or unsoldering the battery, especially if your soldering iron is grounded!

Q How are sounds stored on the DMX/DX?
A Sounds are stored as sampled PCM (Pulse Code Modulated) audio on individual EPROMs. The data format is raw a-law companded. There are no headers or other non-audio data stored on the EPROM. The sample rate varies from about 16kHz to 32kHz, depending on the voice.

Q What are EPROMs?
A Eraseable Programmable Read-Only Memory. This is a form of Integrated Circuit (IC) that is packaged in a ceramic Dual-Inline Package (DIP). EPROMs are erased by shining an ultraviolet light through a transparent window in the part. EPROMs are programmed at the factory, or after erasure using an EPROM Programmer. Once programmed, they will hold their data for 5--10 years before data loss may start to occur. One type of "EPROM" is the OTP (One-Time Programmable). These are electrically identical to EPROMs, but have no window through which to erase the chip. So, they can only be programmed once.

Q Where do I get EPROMs?
A The DMX and DX drum machines use 2732 and 2764 EPROMs. These are getting harder to find these days, as larger capacity devices such as 27256 EPROMs are more common. But, they can still be found at many major electronic distributors and surplus houses. Search the web. Typical part numbers are similar to 27C32, 27C64, 2732A, etc.

Q How do I program EPROMs? What hardware do I need?
A A blank EPROM (Erasable Programmable Read-Only Memory) can be programmed with the aid of a computer peripheral called a "burner", "EPROM programmer", or "device programmer". Get yourself one of these, connect it to your computer, and follow the instructions that come with it. To convert a WAV file into a format that can be programmed onto an EPROM for use in the DMX or other companded format machine, use the WAV2DMX program on an appropriate WAV file. Then, program the resulting binary file onto the EPROM.

QHow do I erase EPROMs?
A With an EPROM eraser. This is a device that exposes the EPROM chip to ultraviolet light, which will erase it and make it able to accept a new sound. Note that "OTP"e; EPROMs are packaged in a solid plastic package, rather than the ceramic package with a window, and cannot be erased and reprogrammed.

FAQ maintained by Paul J. White. Feel free to submit corrections and other DMX-related questions.