A2DP AAC codec bandwidth
A2DP AAC codec bandwidth
- Subject: A2DP AAC codec bandwidth
- From: Feng Yu Hong <email@hidden>
- Date: Thu, 21 Jan 2016 03:13:08 +0000
- Thread-topic: A2DP AAC codec bandwidth
IOS devices support SBC and AAC codec in A2DP profile. We measured the bandwidth of AAC codec by playing 20~20kHz log sweep sine wave signal. We
tested three iPhones ( iphone4S: ios
6.1.3; iphone5: ios8.1.3 iphone6 ios9.2). We compared two Bluetooth headphone (one uses CSR8635 chip, another uses our own chip). CSR’s bandwidth is 20kHz, but our chip’s bandwidth is 17.5kHz. We captured Bluetooth communication data through
Ellisys Bluetooth analyzer. We have excluded AAC decoder of Bluetooth headphone. AAC encoder of Iphone sends the different bitstream when it connects the two headphones. But AAC codec capabilities of the two headphones are the same, and the negotiated AAC
capabilities through AVDTP are the same. The negotiated AAC format is listed.
Media Codec Type MPEG-2,4 AAC
Object Type MPEG2 LC
Sampling Frequency 44.1kHz
Channels 2
Variable Bit Rate Yes
Bit Rate 262 kb/s
The issue seems to involve a configure parameter of aac bandwidth (or cutoff frequency). But A2DP doesn’t define the configure parameter of bandwidth,
and only define the configure parameters of object type, sampling frequency, channels, VBR and bit rate.
Does IOS use private parameter that isn’t defined by A2DP? CSR chip seems to know this private parameter.
Yuhong
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