Hi everybody,
I have been using speex-1.2beta1 and my input data is 8-bit unsigned so I
know that I should convert from 8 to 16 bits. I've done the convertion as
following.
for(int i=0; i<160; ++i)
{
input_frame[i] = (short)( (data[2*i] << 8) | data[2*i+1]);
}
When my codec application didn't work right, I think that the reason is an
error at this convertion. For this aim, I looked at read_samples function in
speexenc project and I can't understand why the convertion is done in this
way:
for(i=frame_size*channels-1;i>=0;i--)
{
s[i]=(in[i]<<8)^0x8000;
}
(in my application, channels is 1 and frame_size=160)
I can understand why shift left 8, but can't why we should do XOR operation
with 1000 0000 0000 0000. Should I do the convertion operation so and why?
Please can you clarify? Thanks a lot for your helps.
Sincerely
Yasemin
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I?d say this is out of scope for this mailing list. Any how, you can?t
just shift a signed number by 8 (multiplying with 256) without handling
the signedness-bit.
PCM 16-bit samples are stored as signed values.
Try something simpler which works first and then optimize your code
afterwards.
unsigned char inSamp;
short s1, outSamp;
s1 = (short) inSamp;
s1 -= 128;
s1 *= 256;
outSamp = s1;
It?s probably possible to reduce the complexity of this using bitshifts,
unless you know what you are doing and are in a lot of need for speed I
don?t see the reason.
//JT
//JT
-----Ursprungligt meddelande-----
Fr?n: speex-dev-bounces@xiph.org [mailto:speex-dev-bounces@xiph.org] F?r
yaseminyilmaz
Skickat: den 15 december 2006 17:46
Till: speex-dev@xiph.org
?mne: [Speex-dev] About "Convert 8->16 bits"
Hi everybody,
I have been using speex-1.2beta1 and my input data is 8-bit unsigned so
I know that I should convert from 8 to 16 bits. I?ve done the convertion
as following.
for(int i=0; i<160; ++i)
{
input_frame[i] = (short)( (data[2*i] << 8) | data[2*i+1]);
}
When my codec application didn?t work right, I think that the reason is
an error at this convertion. For this aim, I looked at read_samples
function in speexenc project and I can?t understand why the convertion
is done in this way:
for(i=frame_size*channels-1;i>=0;i--)
{
s[i]=(in[i]<<8)^0x8000;
}
(in my application, channels is 1 and frame_size=160)
I can understand why shift left 8, but can?t why we should do XOR
operation with 1000 0000 0000 0000. Should I do the convertion operation
so and why? Please can you clarify? Thanks a lot for your helps.
Sincerely
Yasemin
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Note that most 8-bit formats are not "linear", but use a logarithmic scale like u-law or A-law. In that case, the conversion is more tricky, but I'm sure there's code somewhere to do it. Jean-Marc yaseminyilmaz a ?crit :> > > Hi everybody, > > > > I have been using speex-1.2beta1 and my input data is 8-bit unsigned so I > know that I should convert from 8 to 16 bits. I've done the convertion as > following. > > > > for(int i=0; i<160; ++i) > > { > > input_frame[i] = (short)( (data[2*i] << 8) | data[2*i+1]); > > } > > > > When my codec application didn't work right, I think that the reason is an > error at this convertion. For this aim, I looked at read_samples function in > speexenc project and I can't understand why the convertion is done in this > way: > > > > for(i=frame_size*channels-1;i>=0;i--) > > { > > s[i]=(in[i]<<8)^0x8000; > > } > > > > (in my application, channels is 1 and frame_size=160) > > > > I can understand why shift left 8, but can't why we should do XOR operation > with 1000 0000 0000 0000. Should I do the convertion operation so and why? > Please can you clarify? Thanks a lot for your helps. > > > > Sincerely > > Yasemin > > > > > ------------------------------------------------------------------------ > > _______________________________________________ > Speex-dev mailing list > Speex-dev@xiph.org > http://lists.xiph.org/mailman/listinfo/speex-dev