Frequency, despite critical acclaim and the gathering of a fairly devout following, was not the financial success that SCEA likely had in mind for Harmonix's first project. Fortunately, two years later, they got another chance. Amplitude was, for all intents and purposes, a sequel to Frequency. Despite getting a complete makeover visually and musically, the core gameplay in Amplitude is the same as it was in Frequency. The game still handles the same way, and melodies are still created by hitting notes along predetermined paths to create a song segment-by-segment.

One key difference between the two games is the music. While Frequency's songlist was almost completely composed of electronic music, its successor goes for a far more diverse array of genres. In addition to a handful of techno and trance music for Frequency veterans, Amplitude also includes styles of music ranging from pop-punk, to alternative, to hip-hop, and even hardcore metal. As is expected of a sequel, Harmonix's second project also received a complete visual makeover. Instead of continuing through static arenas where the only difference between songs were the assorted images, each of Amplitude's sections takes place in a completely different 'world', of which individual songs showcase a different segment.The arenas were made more detailed, colorful, and also utilize full-motion video in several sections(as displayed on screens in the background, similar to Frequency's), many contributed from the respective artists' own videos.

From time to time, certain arenas can offer complications similar to some of Frequency's more complex-pathed stages: unpredictable directions. Some of Amplitude's arenas carry the tracks skyward at a tangent similar to ascending a roller coaster, which can make the correct timing of oncoming notes frustrating at best. For avatar purposes, Amplitude also uses a more graphically advanced, but less creativity-driven, character creation process. Similar to the types of models used in their current projects, the Amplitude avatars are made by selecting assorted faces, body types, outfit accessories, and other characteristics to create the player's appearance.The avatar also plays along with the song and track currently being controlled, and will be shown playing the instrument of the present section.

While the core gameplay between Amplitude and Frequency is basically the same, some variations were made to lessen the random nature of Frequency's song courses. When an instrument's section in Frequency was completed, there was still a high probability of the same track coming up in the very next section, even if it had been just completed only moments prior. In Amplitude, if a instrument's track is completed, it will always vanish for the same set amount of time. This can be both a benefit and a detriment. Completing every track in a Frequency song would often lead to continual sections of no notes whatsoever; simply prolonged opportunities for the player to 'freestyle' the completed song. Occasionally this would only go on briefly; sometimes it could last the entire final section of a song. is made passing a song much easier, it also made it harder to keep up a high score, since completing note charts are worth far more points than freestyle segments. In Amplitude, the notes will constantly return to challenge the player until the very end of the song(usage of powerups aside). However, the strict pattern-based nature of Amplitude's note repetition can also make it difficult to maintain a chain, since a player may be required to link two instruments that are on completely separate sides of the arena, if all the ones between them haven't regenerated yet.While it is possible, it can be very difficult to effectively pull off.

For the most part, Amplitude's power-ups are exactly the same as Frequency's. The Autoblaster returns, as the familiar green square, letting players eliminate a complete track of instrument notes in one shot. Freestyle has also made a come back, depicted as a blue triangle, though it functions a little differently than it did in Frequency. Instead of creating a melody with assorted scratch instruments on a blank track, Freestyle completely removes all the tracks from play, and the player controls a disembodied spark of energy, which creates random scratch and music effects along the resulting empty space, while drawing assorted patterns and pathways. Freestyle still remains one of the most valuable power-ups for evading a particularly difficult set of notes.

Multiplier functions the same, depicted as a yellow star. When used in conjunction with a high note-collect streak and Freestyle, it can rack up an almost unbeatable amount of points. The new power-up in Amplitude is the Slow-Mo. Depicted as a purple square, Slow-Mo reduces the speed of the song to half for a short duration of time. While not as valuable as Autoblaster or Freestyle, this is the next best thing, since even the most ridiculous of note-charts can be read easier with this item in play.

Amplitude (PlayStation 2)

As Amplitude's front cover attempts to make obvious at a glance, the game contains one eclectic soundtrack. Like Frequency, certain songs are only playable on higher levels. The second-to-last world can only be played on Hard('Brutal'), and the final world is only accessible on Expert('Insane'). Another notable difference between Frequency and Amplitude is the addition of the 'Boss Song'. Each world has three songs to begin with. Once those three are completed, the player will then be revealed the identity of the Boss Song. If the player completes all four with a high enough score, then the player can unlock the Bonus Song. The Bonus is completely optional, but the Boss Song must be completed to continue to the next world.

There's also a notable demo disk for Amplitude. P.O.D.'s third-to-last album, their self-titled one, came with a bonus disk that was a single-song 'demo' for Amplitude. This is a bonus P.O.D. song which is actually pretty difficult.

When all's said and completed, much like its predecessor, Amplitude still offers the option of remixing any song from its soundtrack. Additionally, it offered the option of playing online against other players, with several exclusive 'attack' power-ups to use against the competition, but to the best of my knowledge, finding players online is not a common occurrence nowadays.

Did Amplitude deliver in ways Frequency didn't? In several ways, definitely. Unfortunately, it did not deliver a financial success. While both games received critical acclaim and maintain a devoted following, many of whom still wait and hope for a third game in the series, the series never achieved the widespread popularity of both the Guitar Hero and Rock Band series that eventually made the Boston developers at Harmonix a household name.

It's unlikely the 'FreQ' community will ever receive the third game that has been years in the waiting (even rumored to have been called 'Wavelength' at one time), due to Sony having rights to the Frequency/Amplitude series. The closest is Harmonix's own Phase for the iPod, which automatically generates note patterns based on the song being played. On the bright side, there's still two games that remain as intense and innovative as they were from day one, and if nothing else, they gave Harmonix their first steps toward taking the music gaming industry by storm.