Re: A2DP AAC codec bandwidth
Re: A2DP AAC codec bandwidth
- Subject: Re: A2DP AAC codec bandwidth
- From: Feng Yu Hong <email@hidden>
- Date: Tue, 03 May 2016 02:22:37 +0000
- Thread-topic: A2DP AAC codec bandwidth
Thank for your reply.
I know AAC codec is perceptual codec, and subject listing test is best method of measuring perceptual quality. But lots customers
take the codec bandwidth as an important objective evaluation index.
Is it possible that measuring codec bandwidth reaches 20kHz on IOS 9.2 if setting MTU value is more than 895 byte?
Yuhong
发件人: email@hidden [mailto:email@hidden]
发送时间:
2016年4月30日 8:34
收件人:
Feng Yu Hong
抄送:
email@hidden
主题: Re: A2DP AAC codec bandwidth
How are you measuring quality? I’m not a codec engineer, but I would imagine you need a psychoacoustic test to measure “quality”. Bitrate or sample rate alone can tell
you the data pattern, but it’s very possible that the AAC encoder has improved over time and can now encode the same data with similar or better perceived quality at the same or lower bitrates.
On Apr 28, 2016, at 8:22 PM,
Feng Yu Hong <email@hidden> wrote:
I have read the technical note tn2271. but I don’t know the difference between ios 6.1.3 and
ios 8.3 (ios 9.2). MTU size that we used is 895 byte. The quality of aac bitstream in ios 8.3 and ios 9.2 is not as good as the quality in ios 6.1.3.
The AAC codec is always configured as 44100Hz, but the MTU determines the max packet size that will be encoded. You can read about the encoder here. The encoder is configured
as kAudioCodecBitRateControlMode_Variable.
On Apr 12, 2016, at 3:26 AM,
Feng Yu Hong <email@hidden> wrote:
We have modified MTU size from 672 to 895. Iphone 4s (ios 6.1.3 )
can be up to 20kHz bandwidth. But Iphone4s( ios 8.3) and iphone6( ios 9.2) only be up to 18.9kHz bandwidth. CSR8635 has the same issue.
Is it possible that AAC bandwidth can be up to 20kHz, rather than 19kHz in a high version of the ios system?
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