Game Boy Sounds in Pokémon HeartGold/SoulSilver? Not Possible — Different Audio Engine

You cannot get the original Game Boy sound effects in Pokémon HeartGold/SoulSilver.

Why

• HG/SS run on Nintendo DS hardware with a completely different audio engine.
• No in-game option to switch sound fonts.

Alternatives for Nostalgia

• Listen to the original Pokémon Red/Blue/Yellow soundtracks (YouTube, Spotify).
• Play the originals via Game Boy emulator (legal if you own the cart).
• Fan-made ROM hacks exist that replace HG/SS sounds with GB versions — use at own risk (not official, may break saves).

The DS games have their own excellent orchestrated soundtrack — give it a chance!