Before Proto-Sound 2.0 and 3.0 there was the original Proto-Sound system (also known as Proto-Sound 1 in the marketplace) and Loco-Sound. Both are briefly detailed below.
Original Proto-Sound (Proto-Sound 1)
The original Proto-Sound®
system was a complete onboard CD-quality digital sound and conventional train control system that utilized a microprocessor which allowed users to program and activate sound files and train control features in locomotives equipped with it. It was found on many M.T.H. O Gauge 3-rail locomotives produced between 1995 and 2000 but was retired in mid-2000 in favor of Proto-Sound 2.0 and Loco-Sound. It requires no additional equipment to a layout and can be controlled with most AC transformers equipped with a bell and whistle/horn button.
The original Proto-Sound system does not include a command control receiver allowing for independent locomotive control found on many modern command control equipped locomotives (like those equipped with Proto-Sound 2 or later), however it does allow remote operator control over a variety of locomotive functions including remote access of Proto-Couplers from anywhere on the layout, the ability to lock a locomotive into a directional state (forward, neutral or reverse), trigger passenger or freight yard sound effects and more.
Access of the various functions and sounds required the user to trigger the features using a series of throttle movements and presses of the bell and whistle/horn buttons on compatible AC transformers. Depending on its state, the Proto-Sound onboard locomotive circuit would respond to these tranformer actions and que the locomotive to activate the desired feature or sound. In certain states, the locomotive even provided the user with audible feedback - in the form of a series of clink and clank sound effects - that confirmed the user had entered the desired state or feature.
M.T.H.'s Loco-Sound system was developed in parallel with the firm's Proto-Sound 2.0 system in the late 1990s and debuted in M.T.H. RailKing ready-to-run train sets in the 2000 product line. Unlike the original Proto-Sound system of the 1990s, Loco-Sound's digital sounds were somewhat limited providing standard locomotive sounds (steam chuff or diesel "roar), whistle/horn and bell sounds. These digitally developed sounds brought more realistic digital sounds and some remotely accessible train control features to inexpensive O Gauge 3-rail train sets and locomotives. It is perfect for the beginning model railroader or people on a budget.
Unlike the original Proto-Sound system, Loco-Sound equipped locomotives featured an innovative speed control system that allowed locomotives to maintain their speed as determined from track voltage even when encountering grades, curves or loads. Functioning similarly to an automobile's "cruise control" system, the Loco-Sound circuitry would increase power to the locomotive's motor(s) when it sensed the train slowing down or reduce power to the motor when it sensed the locomotive speeding up (as if coming down a hill). The speed control functionality significantly increases the "play value" of Loco-Sound equipped locomotives because the trains were now capable of operating in a much more realistic manner and no longer required constant attention from the transformer throttle to manage its speed.
As with the original Proto-Sound system, Loco-Sound does not provide onboard command control functionality for locomotives it is equipped in.