Why are instruments interrupted during pausing?

[predcon]

You know when you're playing a game on an old system, and you pause to do something, then you unpause, and one of the instruments in the BGM that's playing is silenced for whatever note it was playing, and then picks up again a second after? What causes that? Why one instrument and not all?

[Garpocalypse]

Kind of a broad question that spans many different sound chip manufacturers but usually it's because of the limited polyphony that the old sound chips were capable of.  Taking the Genesis for example the yamaha 2612 sound chip that was in that system was only capable of six simultaneous voices.  That's 6 channels that needs to be split between music and any sfx so chances are the game at any given time is hitting the maximum amount of polyphony it can handle.  Now, if a game uses a "pause"/"unpause" sound effect that requires a single channel to play.  In order to play the sound effect something has to go at least for the duration that the pause sound effect plays at which point the missing voice can come back in. 

You can usually hear this throughout a lot of 8 and 16 bit games when a lot is happening on screen, parts of the background track are dipping in and out.  Juggling your different voices in an effective way that doesn't detract from the game was a necessary skill to have for a game composer back in the day.  

 

 

[predcon]

I'd figured it was an instrument/voice limit issue, just wasn't sure how the chip decided which one to suspend.