Thanks Dejun. By the way, so if I pack the actual encoded bits on a per frame
basis and save it as a .amr file, then would any player that plays 3GPP format
audio files be able to play them? I plan to try this out anyway, but just wanted
to know if the file would be recognized as a 3GPP content or is there some other
processing that is done on this before it can be recognized and played in any of
the 3G mobile phones?
Cheers,
Ashwin
----- Original Message ----
From: 德军
To: Ashwin Chandrasekaran ; Rama Krishna K
Cc: s...
Sent: Tuesday, August 5, 2008 6:50:20 PM
Subject: 答复: [speechcoding] AMR-NB codec
Hi,Ashwin,
The reason is that,for each bit of the output of AMR-NB encoder is
represent by a WORD,for example, "0X81" represents "0",and "0X7F" represents "1"
in the bitstream.For example,if u use MR122 mode to encode a speech file. you
will get 244 bits per frame,but in each frame,each bit will be changed into
"0x81" or "0X7F".So the output of encoder will be bigger than the input.maybe
you can find more details in 3GPP website or ITU-T website.
Hope this will
help u.
Regards,
Dejun
________________________________
发件人: s...
[mailto:s...] 代表 Ashwin
Chandrasekaran
发送时间: 2008年8月6日 04:32
收件人: Rama Krishna
K
抄送: s...
主题: Re: [speechcoding]
AMR-NB codec
Hi
Rama,
Sorry about the confusion. I actually meant the file at the output
of the AMR-NB encoder alone (not the decoded output) . Anyway, thanks for taking
time to answer my questions.
Cheers,
Ashwin
-----
Original Message ----
From: Rama Krishna K
To: ashwin_c29
Cc:
speechcoding@ yahoogroups. com
Sent: Monday, August 4, 2008 11:24:44
PM
Subject: Re: [speechcoding] AMR-NB codec :
Hi Ashwin,
Please
find answers below.
Regards,
Rama
On 03/08/2008, ashwin_c29
wrote:
>
> Hi All,
>
> Had a small doubt regarding the
AMR codec.
> Why is the file size (file
> obtained at the output of
an AMR-NB codec) constant for all AMR rates
> even though there is a
different bit allocation for each 20 ms speech
> frame of the input file
corresponding to each of these rates.
[Rama]: AMR-NB codec contains both
Encoder and Decoder.
Encoder encodes each 20ms speech frame to corrresponding
bit rate
specified at the encoder.This is the place where compreesion
happens.
for example if you are encoding using 12.2kbps,same 20ms will
be
represented by 244 bits.
At the decoder,using these 244 bits we get 160
samples (20ms * 8Khz).
>(Besides the file size is also larger than
that of the input file).
[Rama]: So once it got decoded the file size should
be same as input file.
But perceptually both will be same.
> Am
still a novice as regards this codec and haven't been able to figure
this
out.
> It would be nice if someone could throw some light on
this.
>
> Thanks,
>
Ashwin.