Hello,
I (try to) use the SBC package inside btsco 0.42 and want to
give some feedback on things I noticed:
SBC in general
--------------
Compared to the Philips reference en/decoder, the
decoded sound using the floating-point version
is much more quiet.
The USE_FIXED version is even more quiet (a (signal-disturbing)
"<<= 2" operation seems to bring the signal to about the original
level, so it is really quiet).
How much MIPS does the implementation needs?
I read that once some Philips guy told something
about 5 MIPS, but it was not clear what types of
MIPS he meant nor to which version this applied.
Compared to MP3 encoding and decoding, what are your
experiences?
sbcenc.c
--------
bug?: Files of a size <= the buffer size (i.e. 2048)
are not processed.
bug?: not all option shortcuts (-* forms instead of --*) can
be used (also holds true in sbcdec.c).
feature: I wrote (imperfect) sbcenc and sbcdec versions that consume and
produce canonical .wav files, respectively.
Is somebody interested?
----addendum 1-----------------------------------------
Proposal to add at least some lines
to the important functions:
int sbc_encode(sbc_t *sbc, void *data, int count)
----------------------------------------------
Encodes PCM samples into one frame of SBC-encoded data. The PCM samples
starts at data and are of length count. The encoded data
is of length sbc->len is then stored in sbc->data.
Returns the length of the encoded PCM data
Please note that for encoding an entire stream, you might
have to use sbc_encode multiple times as it encodes only
into 1 frame per call.
int sbc_decode(sbc_t *sbc, void *data, int count)
----------------------------------------------
Decodes one frame of SBC-encoded data. The SBC-encoded data
starts at data and is of length count. The decoded data
of length sbc->len is then stored in sbc->data.
Returns the length of the frame that was decoded.
Please note that for decoding an entire stream, you might
have to use sbc_decode multiple times as it decodes only
1 frame per call.
Regards,
Fritz
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Fritz
I'm glad someone is having a look. Yes, we have some work to do here.
fyi, we're trying to limit changes to the fixed-point only version in
the sbc sourceforge project. It does have volume problems but we'd like
to hammer them out so fixed point is what everybody uses.
> The USE_FIXED version is even more quiet (a (signal-disturbing)
> "<<= 2" operation seems to bring the signal to about the original
> level, so it is really quiet).
there are some ops like this that are to avoid fixed point overflows.
when the encoder overflows, it generates an annoying "pop" noise in the
stream.
> How much MIPS does the implementation needs?
> I read that once some Philips guy told something
> about 5 MIPS, but it was not clear what types of
> MIPS he meant nor to which version this applied.
> Compared to MP3 encoding and decoding, what are your
> experiences?
I haven't measured it and I've only tried it on a pxa255 at 400mhz but I
think someone had success with an arm 7...
> sbcenc.c
> --------
>
> bug?: Files of a size <= the buffer size (i.e. 2048)
> are not processed.
that would explain why some songs end prematurely
>
> bug?: not all option shortcuts (-* forms instead of --*) can
> be used (also holds true in sbcdec.c).
it would be nice to be consistent in the args
>
> feature: I wrote (imperfect) sbcenc and sbcdec versions that consume and
> produce canonical .wav files, respectively.
> Is somebody interested?
sbcenc/dec are part of the "playground" which is there for testing and
development. If your additions make that easier then they'd be nice to have.
>
>
> ----addendum 1-----------------------------------------
>
> Proposal to add at least some lines
> to the important functions:
>
> int sbc_encode(sbc_t *sbc, void *data, int count)
> ----------------------------------------------
> Encodes PCM samples into one frame of SBC-encoded data. The PCM samples
> starts at data and are of length count. The encoded data
> is of length sbc->len is then stored in sbc->data.
>
> Returns the length of the encoded PCM data
>
> Please note that for encoding an entire stream, you might
> have to use sbc_encode multiple times as it encodes only
> into 1 frame per call.
>
>
> int sbc_decode(sbc_t *sbc, void *data, int count)
> ----------------------------------------------
> Decodes one frame of SBC-encoded data. The SBC-encoded data
> starts at data and is of length count. The decoded data
> of length sbc->len is then stored in sbc->data.
>
> Returns the length of the frame that was decoded.
>
> Please note that for decoding an entire stream, you might
> have to use sbc_decode multiple times as it decodes only
> 1 frame per call.
which problems are these proposals addressing?
brad
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Hello Fritz,
On Fri, 15 Sep 2006, Hohl, Fritz wrote:
> int sbc_decode(sbc_t *sbc, void *data, int count)
> ----------------------------------------------
> Decodes one frame of SBC-encoded data. The SBC-encoded data
> starts at data and is of length count. The decoded data
> of length sbc->len is then stored in sbc->data.
At least for the decode function an additional parameter data_len is
required to avoid destination buffer overflow on malformed packets.
Ciao,
Peter
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