Question for the experts please:

For recording on-the-fly directly to MP3 (such as can be done on line-in for some MP3 players), if the source material is the same and the encoder is the same etc, does it require MORE or LESS processing power to record at high bitrate compared to low bitrate? Just to make it clear: if I record at 256k does it need more or less processing than if I record at 64k?

My thinking would be that low bitrate needs more compression and therefore more processing power, but I don't have a good understanding of what's involved. Am I right?