Apple

I have expanded the A2DP capabilities of a Bluetooth SNK to support AAC. I am using an iPod Gen4 with iOS 6.

Things are working well except for one issue. A particular song (“Time” from Pink Floyd’s Dark Side of the moon) when encoded at 256kbps. I am seeing the AAC packet rate slow down and I think it is actually dropping packets. Because of this packet rate slow down, unless I buffer about 25 AAC packets before playback starts, I starve the buffer feeding my D/A converter.

This same song works fine if I put a version on the iPod that has been encoded using 128kbps.

I am thinking the issue is related to the MTU value being used in the channel. The Apple BT Developers Guide recommends using a MTU value of 885 bytes. The max packet payload size I see coming across is 880 bytes. HOWEVER, I know that there are about 20 packets in this song, during the problem area (starting at the 20 second mark) which are > 885 bytes. What will the iPod do if it encounters a packet that is larger than the Channel’s MTU value? Does it split it up or just not send it?

Anyone else see this issue?

thanks

Shawn K. Steenhagen

Software Specialist

Applied Signal Processing, Inc.