aptX support different modes, but not all of them can run within the constraints of a Bluetooth link. There simply isn't enough bitrate in the old Bluetooth for

aptX support different modes, but not all of them can run within the constraints of a Bluetooth link. There simply isn't enough bitrate in the old Bluetooth for uncompressed audio. If there was enough of it, you wouldn't need aptX or any other specialty codec, you would just run PCM and that's it. Even ADPCM at half the bitrate would be a big improvement (particularly, for latency), but there is not enough bitrate even for that.