For those unfamiliar with Frequency, it and its sequel Amplitude are a frantic hybrid of puzzle game and music/rhythm game. The games derive their unique gameplay from a simple premise: Tap buttons to match onscreen indicators with the right timing to create musical samples and slowly bring together a full song, one instrument at a time. In the original Frequency, the playfield was an octagonal "tunnel." In Amplitude, this "tunnel" has been replaced with a "highway" of 6-7 tracks, depending on the song. Each track represents a different musical instrument (such as guitar or drums) or element of the song (such as vocals or synth effects). Each song is broken down into 4 or more sections, with each section's tracks broken up into 16 or more bars.

Guiding a 3-pointed "Beat Blaster" and using the square/triangle/circle or L1/R1/R2 buttons (to fire and release notes on the left center and right channels respectively) and successfully completing two bars on a track will lock it down so that it will play by itself for another 8 bars. Moving the directional pad left or right will slide across the "highway" of tracks. So, by moving back and forth across the playfield locking down tracks in succession, you're essentially mixing the song together in real-time--adding vocals or guitars to the background beat of the song so that the song becomes complete. This may sound easy, but it is challenging because of an added gameplay element--an energy meter which is an approximation of how well you're playing the song. Locking down bars in succession will keep the meter full. Failing to lock bars down will result in energy loss, until the meter is empty and the song ends.

Amplitude also has a scoring system, which comes into play not only for the old-school thrill of trying to get a high score, but also acts as the key to unlocking the game's 5 boss songs and 6 secret songs. Continuous, uninterrupted streaks of locking tracks will queue "multipliers," which are added for each track in succession up to a maximum of 8 times the value of the notes in a bar. Thus, the primary goal is to complete the song, and the secondary goal is to earn enough points to unlock the secrets. The game also adds in several power-ups, randomly scattered in various places throughout each song to assist players. Amplitude adds a new "Slo-Mo" power-up, which slows the song's beats-per-minute (BPM) down in real-time, to allow players to handle especially tough sections.

Amplitude improves upon Frequency's gameplay in several areas. While many hardcore Frequency fans (known as "FreQs" lamented the change from "tunnel" to "highway," the latter actually improves the player's ability to see the entire playfield and quickly identify which tracks to move to next. To assist player's in maintaining their multiplier streaks, the game places large green arrows with a multiplier value pointing down over upcoming available tracks. Another helpful feature is the audible metronome "ticks" that help a player hear the backbeat of the song easier if they begin to miss several bars in a row.

Without a doubt, Harmonix has done a fantastic job of increasing Frequency's already colorful and fluid visuals with Amplitude's incredibly active arenas and environments. In a nod to Sega's classic (and also grossly underappreciated) PS2 music/rhythm shooter Rez, Amplitude's game arenas and game menus now flow together in a vast network of highways, tunnels and bridges, crossing through futuristic cities and landscapes. The amount of activity in the 3D environment behind the playfield is impressive, from giant TV screens showing video clips of the music artists in the game to flying cars and exploding power grids.

As in Frequency, Amplitude includes, Solo and Multiplayer Game and Remix modes. Online gameplay (Multiplayer, Duel and Remix modes) is also standard with Amplitude (Frequency was online-enabled through the PS2 Network Adaptor's demo disc). Solo mode is the standard campaign, offering 4 difficulty modes: Mellow, Normal, Brutal and Insane. Completing each mode will unlock new arenas, new Freq parts, and of course, new songs. Multiplayer pits two to four players against each other in a fullscreen battle royale. Amplitude adds the Duel mode to Multiplay and Online. Duel mode allows two players to play a game of "Horse" by challenging each other to complete increasingly difficult sections of notes.

Remix mode adds a heavy dose of replayability to the title by allowing players to take existing tracks and lay down notes and apply several special sound effects to them, creating a new sound for a song using it's existing sound samples. Amplitude's online mode has been vastly improved since the original Frequency's hastily-added online option. Taking a cue from the Xbox Live service, a ranking system has been added, as well as the ability to search for buddies online. Perhaps the greatest new online feature is the Online Remix Repository, which contains SCEA/Harmonix's hand-picked selections of the best of player remixes (submitted by players using the Upload Remix option). Harmonix has also mentioned that there will be several remixes made available from the songs' artists.

Of course, the most important element of the game is the music itself, and in this area Amplitude manages to succeed admirably in providing a diverse range of musical genres without feeling incohesive. Techno, rock, rap, electronica, jazz, funk, and eclectic fusions of all of the above are represented in the games' 26 songs. The complete musical selection includes such well-known (and some lesser known) music artists: Garbage, Weezer, Blink 182, David Bowie, Run DMC, Pink, Papa Roach, Herbie Hancock, BT, The Baldwin Brothers, P.O.D. (remixed by The Crystal Method) and others. While some Frequency fans may be disappointed to see some marquee electronic artists from the original game missing in Amplitude, they can rest assured that the game still provides plenty of excellent electronic music. Upon completing each song, the player can then listen to it in its entirety using Amplitude's new Soundtrack mode.

Overall, Amplitude manages to be easy enough for beginners to learn but challenging enough to give jaded FreQs an adrenaline rush. The sequel is superior to the original in every way, and retains its charm while creating a new direction for the series to follow. It is without a doubt one of 2003's best titles, not only for PS2 but across all platforms. PlayStation 2 owners should have a copy of Frequency and Amplitude on their shelves, both come highly recommended.