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Hi,
I am using a codec with sampling frequency of 32KHz, I am decimating the input
to get 8KHz frequency. These samples are then fed into the MELP Analysis. The
ouput of melp analysis is transmitted through a modem to the remote side. Here
MELP Synthesis is called, and the speech is played by codec. I have 2 questions
here,

1. As the data is being transmitted to remote side, there can be some
corruption. Is it possible that melp synthesis variables gets so badly
corrupted, that after synthesizing these corrupted frames, it cannot synthsize
correct frames too???

2. If I give a sinosidal waveform, for the sake of testing my codec amplitude
etc, what output should I expect. One thing I am sure about is that it wont be
sinosidal, as melp is designed for speech, but still I would like to know what
should be its output?

Thanks and Regards,
Saba

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Saba-

> I am using a codec with sampling frequency of 32KHz, I am decimating the
> input to get 8KHz frequency. These samples are then fed into the MELP
> Analysis. The ouput of melp analysis is transmitted through a modem to
> the remote side. Here MELP Synthesis is called, and the speech is played
> by codec. I have 2 questions here,
> 
> 1. As the data is being transmitted to remote side, there can be some
> corruption. Is it possible that melp synthesis variables gets so badly
> corrupted, that after synthesizing these corrupted frames, it cannot
> synthsize correct frames too???

If transmission errors affect the sync bit, then you might not get valid
synthesis
results until after several consecutive frames go through with no errors.  It
can
take several hundred msec for the MELPe algorithm to re-acquire sync at 2400
bps.

> 2. If I give a sinosidal waveform, for the sake of testing my codec
> amplitude etc, what output should I expect. One thing I am sure about
> is that it wont be sinosidal, as melp is designed for speech, but still
> I would like to know what should be its output?

A sine waveform will sound garbled, not like anything I can describe.  Just
will
sound bad.

-Jeff

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Thanks for your reply.
The problem that I am facing is that after processing some corrupted frames MELP
sysnthesis starts giving complete silence at the output. The thing that puzzles
me is that it is not recovering from the errors, as I am sending one saved
packet of DTMF tone. I have observed that even when melp starts receving the
correct from it does not recover. As I am using the same frame at each interval,
is it possible that it is not finding the sync bit right and never re syncs
again.

>From the output of the sinosidal wave, I mean that if I want to see the
output waveform on an oscilloscope after passing the digital data through MELP
and DAC, what kind of wave form should I expect???

Thanks and Regards,

Saba

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Saba-

> Thanks for your reply.
> The problem that I am facing is that after processing some corrupted frames
MELP sysnthesis starts giving complete
> silence at the output. The thing that puzzles me is that it is not
recovering from the errors, as I am sending one
> saved packet of DTMF tone. I have observed that even when melp starts
receving the correct from it does not recover.
> As I am using the same frame at each interval, is it possible that it is
not finding the sync bit right and never re
> syncs again.

I don't know.  It should recover, as long as your frames are correctly
formatted, including sync bit.  The classic
test is to use a serial bitstream transmission method (e.g. RS-422), pull the
connector (upon which MELPe synthesis
output becomes garbled, "helicopter noise", etc), then reconnect. 
After a half second to several seconds, it should
be back in sync and reconstructed results sound good.  It shouldn't matter what
junk was received in the interim.

As far as losing sync, how are you sending frames?  Is it a serial bitstream? 
You can't lose sync if you're always
sending frames on byte boundaries, for example bus type of interface.  It has to
be bit-by-bit.

> From the output of the sinosidal wave, I mean that if I want to see the
output waveform on an oscilloscope after
> passing the digital data through MELP and DAC, what kind of wave form
should I expect???

Nothing that can be defined.  Just junk.

-Jeff

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