Displaying 20 results from an estimated 2000 matches similar to: "Description of MDCT"
2001 Jun 10
0
Modified discrete cosine transform
I am trying to learn something of the algorithms used in
Vorbis. One of them is the "Modified Discrete Cosine
Transform" (MDCT). I have found a couple of books with brief
descriptions of the DCT, but almost nothing about MDCT.
(1) is there just one Modified DCT, which can be
expected to be the same whenever someone uses that
name, or does it just mean that you have changed
2017 May 03
0
MDCT implementation and his overlapped relationship
Dear all
In the paper section describes how CELT and SILK had implemented a look/up
head delay of (2.5ms), (5ms) respectively , could you explain me>
1) those values are fixed.
1) how you guarantee those values independent of the architecture's
performance.
Thanks so much
On Tue, Apr 18, 2017 at 10:05 AM, Diego Alejandro Parra Guzman <
daparrag at correo.udistrital.edu.co>
2002 Mar 19
1
mdct as hardware
Hi vorbis-dev!
I'm working with Pattara in the oggonachip project, and wondering about
the implementation of mdct.c as hardware. According your recomendations
about using the floating point version, I would say, we have to implement
the integerized
version of mdct as a core, and use the fpu only to round the input
values. By doing
that, you think the result would be still acceptable?
How
2003 Jul 12
1
mdct query
Hi,
I have a doubt regarding MDCT window size for OggVorbis decoder.
Can the MDCT window size vary from 64 samples to 8192 samples?
Specification says that "legal frame sizes are powers of two from
64 to 8192 samples" .
Is this same as MDCT window size?
Please help me out..
Regards,
shikha
<p>--- >8 ----
List archives: http://www.xiph.org/archives/
Ogg project homepage:
2017 Apr 11
2
MDCT implementation and his overlapped relationship
Dear all
I'm working on the implementation of the MDCT for the processor
ARM-Cortex-M4 I'm trying to replicate the behavior of the MDCT for several
overlapped values however I realized that current implementation of the
MDCT is very close to the theory only in case in which we have and overlap
exactly equal to N/2 where N is the size of the input vector as is shown in
the examples for
2001 Jan 02
0
mdct explanation
...as promised.
This describes the mdct used in my d.m.l patch. I think it is the
same as the Lee fast-dct.
I typed it in a kind of pseudo-TeX, 'cause the ascii art would
kill me. Hope you can read TeX source; if not, ask someone who
can to make a .ps/.gif/.whatever of the TeX output, and put it
on a webpage or something. I'm to lazy to do it (and besides, I
don't have access to TeX,
2013 Jul 08
2
Request for MDCT theoretical reference
Dear Experts,
Can anybody please direct me to proper MDCT theory reference which will
help me understand the code better?
I'm trying to optimize MDCT for a embedded platform. So need good
understanding about theory behind & implementation.
Thanks in advance for your time.
Warm Regards,
Mahantesh
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2000 Oct 20
2
mdct question
Hi,
Can someone tell me which MDCT and invMDCT equation uses? I implemented the
invMDCT one given in
eusipco.corrected.ps file (handed out by Monty way back) and it produces
different time domain samples.
I tried both the FFT method and the slow way directly from the equation and
couldn't reproduce the results
from the original code. This leads me to believe that the forward
MDCT used in
2002 Mar 26
2
size of vectors to be fed to MDCT
Hi,
as we are trying to implement MDCT in hardware, we are caring now about
the "n" (size of input and output vectors to and from MDCT).
As I have looked in the code, this "n" is chosen from the Ogg/Vorbis
stream data in info.c:_vorbis_unpack_info() which means this "n" can vary
aribitrarily (as the power of 2) depending only on the value got from song
data? or is
2013 Jul 11
0
Request for MDCT theoretical reference
http://en.wikipedia.org/wiki/Modified_discrete_cosine_transform is an OK
place to start.
On Mon, Jul 8, 2013 at 7:33 AM, Mahantesh Belakhindi
<girishec28 at gmail.com>wrote:
> Dear Experts,
>
> Can anybody please direct me to proper MDCT theory reference which will
> help me understand the code better?
>
> I'm trying to optimize MDCT for a embedded platform. So need
2002 Aug 21
1
MDCT input and output data blocks
Hi,
I'm trying to determine how the frequency data that is passed to the
MDCT, and output time domain data obtained from the MDCT, is changed
when setting #define MDCT_INTEGERIZED
For instance, the trig array, for a size 256 window begins
1.000000
0.000000
0.998795
-0.049068
0.995185
-0.098017
if INTEGERIZED is set, then it begins
16384
0
16364
-803
16305
-1605
which is simply a left shift
1999 Aug 15
1
Vorbis transform description
OK, into the nitty-gritty, albeit a high-level version. If it sounds
like I'm glossing important details, you're right. This discusses
only the basic DSP; precise coding, framing, sync, etc, will be in
another mail.
Vorbis is a hybrid transform domain general purpose audio encoder,
like MPEG in some respects (it is rooted in much of the same basic
theory). For the most part, the
2005 Feb 20
1
Well decomposed mdct
I did composition of butterfly8 and butterfly16 and I found, that these functions are well decomposed - decomposition doesn't lower computional speed. On the other hand the same can be done with butterfly8 - decomposition to butterfly4 (further decomposition is not possible) but there's no reason to do this. I think little improvement can be done by inlining them. Compiler and processor
2002 Mar 14
1
mdct.c
Hi vorbis-dev,
I'm investigating the mdct* function in libvorbis and writing a small
client program to test it. I found that I have to set ARRAYSIZE when
mdct_init(lookup, ARRAYSIZE) to minimum value of 62 otherwise it will
segfault with mdct_backward.
Is there any lower limit or it is more likely that my code has bug?
Thank you very much,
Pattara
--
Please avoid sending me Word or
2002 Aug 01
2
mdct.h - PI1_8, PI2_8 etc.
In vorbis/lib/mdct.h the following are defined:
for integer:
#define TRIGBITS 14
#define cPI3_8 6270
#define cPI2_8 11585
#define cPI1_8 15137
#define FLOAT_CONV(x) ((int)((x)*(1<<TRIGBITS)+.5))
for floats:
#define cPI3_8 .38268343236508977175F
#define cPI2_8 .70710678118654752441F
#define cPI1_8 .92387953251128675613F
#define FLOAT_CONV(x) = x
Could someone explain where these values
2009 Jun 04
0
Updated MDCT callback patch
Here's an updated version of the MDCT callback patch.
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2011 Aug 01
1
Inverse MDCT formula missing from Specification
Hi
The inverse MDCT formula seems to be missing from the vorbis specification. From reading the source code of stb_vorbis (http://nothings.org/stb_vorbis/) I've a good idea of what it might be, but cannot find the formula anywhere in the official specification (the one on http://xiph.org/vorbis/doc/Vorbis_I_spec.html ). I also understand that the formula stated in the eusipco_corrected.ps
2002 Aug 29
0
yet another MDCT question
mdct.c, lines 436 onward (part of mdct_backward) state
{
DATA_TYPE *oX1=out+n2+n4;
DATA_TYPE *oX2=out+n2+n4;
DATA_TYPE *iX =out;
T =init->trig+n2;
do{
oX1-=4;
oX1[3] = MULT_NORM (iX[0] * T[1] - iX[1] * T[0]);
oX2[0] = -MULT_NORM (iX[0] * T[0] + iX[1] * T[1]);
oX1[2] = MULT_NORM (iX[2] * T[3] - iX[3] * T[2]);
oX2[1] =
2005 Jan 26
2
Butterflies in mdct.c
In mdct.c there's some functions including some-point butterfly. In 32-point and 16-point there are calling of smaller-point function everytime twice on each half of data. When I looked on it I found that's just linear algebra. So it can be rewritten to matrix multiplication. Some one can say: there's optimization on in register working. But imagine there's one calling 32-point,
2000 Oct 23
4
More mdct questions
Sorry for starting another topic, this is actually a reply to Segher's post
on Sun Oct 22 on the 'mdct question' topic. I wasn't subscribed properly
and so I didn't get email confirmation and thus can't add to that thread.
So Segher, if the equation is indeed what you say it is, then replacing
mdct_backward with this version should work, but it doesn't.
Am I applying