[Speex-dev] Shoehorning speex is confusing a newbie

[Michael Jacobson]

This is going to take some explaining and I apologize in advance if any
of this is found in the manual or sample code but I couldn't find it.  I
just graduated last may and this is my first experience with vocoders
and dissecting a professional's code.
 
I work for a company that is currently using a G729A vocoder from a 3rd
party software company and is looking into speex so they no longer have
to pay royalties.  The product we are trying to force speex into is
based on a TI C5416 DSP that did narrowband 8-bit, 8kbs.  The product
was fairly full as it is so some modifications had to be made in order
to fit speex into the project just to allow it to link.  The
modifications are based off assumptions that I made when looking over
the code so I may have been absolutely wrong.
 
The main assumption was about the exc tables.  In looking through
modes.c it appeared that only one table was required for 8kbs so I
commented out the portions of the code that referenced the other tables
and modified "static const SpeexNBMode nb_mode" structure so that the
pointers to the other structures that referenced the tables were NULL. 
We did not have enough data memory to store all the tables.  I thought
this would work with my initialization but when I stepped through the
code in nb_celp for encode it would put it in mode 6 (instead of mode
3), which I believe is 18.2kbs (table 8.2). My set up code is:
 
  st = speex_encoder_init(&speex_nb_mode);
  speex_bits_set_bit_buffer(&bits, &G729_tx, COMPRESS_LENGTH);
  tmp=TESTENC_QUALITY;  //=4
  speex_encoder_ctl(st, SPEEX_SET_QUALITY, &tmp);
  speex_encode_int(st, (spx_int16_t *)samples_in, &bits);
 
which I thought would put it in 8kbs narrowband.  I tried to use
SPEEX_SET_MODE in there too but it just got overwritten by the set mode
in the encode function.  So I thought I'd try to force it into mode 3
and see what happens, and I got A result, but when I try to decode it my
decode stage gets stuck in an infinite loop:
 
while (st->voc_offset<st->subframeSize)
            {
               if (st->voc_offset>=0)
                  exc[st->voc_offset]=sqrt(1.0*ol_pitch);
               st->voc_offset+=ol_pitch;
            }
 
because both voc_offset and ol_pitch is = 0 because this code is never
entered:
 
if (SUBMODE(lbr_pitch)!=-1)
   {
      ol_pitch = st->min_pitch+speex_bits_unpack_unsigned(bits, 7);
   } 
 
This is how I set up the decoder:
 
  dec = speex_decoder_init(&speex_nb_mode);
   speex_bits_set_bit_buffer(&bits, &Speex_enc_buffer[0 +
COMPRESS_LENGTH*Speex_player_frame], COMPRESS_LENGTH);
   tmp=0;
   speex_decoder_ctl(dec, SPEEX_SET_ENH, &tmp);
   speex_decode_int(dec, &bits, (spx_int16_t *)samples_out); 
 
There are some things I am sure will be asked.  Yes I set flags for the
TI_54X part, disable wideband, manual allocation, and fixed point in a
config file and defined the #define value needed to include that config
file.  I do have a heap for the setup of the state structure for encode
and decode and yes I made sure it was big enough to allocate enough to
both.  Yes I destroy the structures after I am done en/decoding them. 
If there is anything you need to help you help me then I am defiantly
willing to share.  I am thoroughly confused and could use some help.
 
Thanks.
 
-Mike Jacobson
michael.jacobson at ultratec.com
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