From Bulbapedia, the community-driven Pokémon encyclopedia.
The GB Sounds (Japanese: ＧＢプレイヤー GB Player) is a type of key item exclusive to Pokémon HeartGold and SoulSilver.
The GB Sounds changes background music to redone 8-bit tracks from Pokémon Gold and Silver and, for some of them, from Pokémon Crystal. It does not affect other audio effects.
It cannot be held as it is a key item.
|| A music player that allows you to listen to nostalgic songs. It's operated with a single switch.
Despite the fact that the GB Sounds tracks are supposed to sound like the original tracks from Pokémon Gold, Silver, and Crystal, none of them sound exactly like the originals. The acoustics sound different and many notes have other pitches. Some tracks had their tempos altered somewhat and other notes in various tracks are not even heard at all. This is due to the games using a soundfont for MIDI playback rather than generating real chiptunes. The different audio hardware between the Game Boy Color and the Nintendo DS should also be taken in consideration.
Several tracks that are absent in the original Pokémon Gold and Silver have received 8-bit remixes. Examples include グローバルターミナル Global Terminal and ４７ばんどうろ Route 47. Despite this, none of the Battle Frontier facilities, except for the outside area and the Battle Tower, have an 8-bit remix of their background music. However, when entered into a Battle Frontier challenge with the GB Sounds activated, the track played during the battle is the GB Sounds version of 戦闘！ トレーナー（ジョウト）Battle! Trainer (Johto). This effect is reverted when battling a Frontier Brain.
Some of the original tracks from Pokémon Gold and Silver, such as the ones pertaining to Team Rocket, オーキドはかせ Professor Oak and オープニング Opening, can be listened to the GB Sounds but not without cheating since, during regular gameplay, the player can only listen to these tracks in their regular versions. To solve this issue, the Pokémon Music Channel hosts the Pokémon Past Archive program every Sunday, which features these tracks in addition to a few others, such as all the Trainer encounter themes.
進化おめでとう！ Congratulations on Evolving!, which also plays when a Trainer successfully catches a Pokémon, is not affected by the GB Sounds in the latter case. Radio music is also unaffected, even though 8-bit remixes of the tracks are available and played as part of the Pokémon Past Archive on the Pokémon Music Channel every Sunday after the GB Sounds is obtained.
If active during a Bug-Catching Contest, the GB Sounds will not switch to the 8-bit version of しぜんこうえん National Park during the contest results; however, it'll perform the switch after the results are announced.
There is also a a glitch associated with the GB Sounds.