michel freiha | 5 Aug 11:12 2010
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Codec Conversion

Dear All,

i would like to ask please if someone tried to make a codec conversion from ilbc to g729, because i did that but the voice quality was too bad and a lot of disconnection..

Can i get your feedback regarding this issue please?

regards

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Tim Nelson | 5 Aug 15:13 2010

Re: Codec Conversion

----- "michel freiha" <michofr <at> gmail.com> wrote:
>
> Dear All,
>
> i would like to ask please if someone tried to make a codec conversion from ilbc to g729, because i did that but the voice quality was too bad and a lot of disconnection..
>
> Can i get your feedback regarding this issue please?
>
> regards

I can't comment on your 'disconnection' as you don't say if that means the call is disconnected or you're getting stuttered audio. Regardless, iLBC has one of the lowest bitrates of the available codecs and as such the voice quality is not spectacular to begin with. Take 'not so good' audio and try to convert it to another audio format, and the deficiencies can be exacerbated.

--Tim
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michel freiha | 5 Aug 21:41 2010
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Re: Codec Conversion

Dear Sir,

I tried to convert ilbc to ulaw and get the same result...Bad Voice Quality

Regards

On Thu, Aug 5, 2010 at 4:13 PM, Tim Nelson <tnelson <at> rockbochs.com> wrote:
----- "michel freiha" <michofr <at> gmail.com> wrote:
>
> Dear All,
>
> i would like to ask please if someone tried to make a codec conversion from ilbc to g729, because i did that but the voice quality was too bad and a lot of disconnection..
>
> Can i get your feedback regarding this issue please?
>
> regards

I can't comment on your 'disconnection' as you don't say if that means the call is disconnected or you're getting stuttered audio. Regardless, iLBC has one of the lowest bitrates of the available codecs and as such the voice quality is not spectacular to begin with. Take 'not so good' audio and try to convert it to another audio format, and the deficiencies can be exacerbated.

--Tim

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Tim Nelson | 5 Aug 21:50 2010

Re: Codec Conversion

----- "michel freiha" <michofr <at> gmail.com> wrote:
>
> Dear Sir,
>
> I tried to convert ilbc to ulaw and get the same result...Bad Voice Quality
>
> Regards
>

Again, iLBC is poor quality to begin with. You can't take a poor audio sample and make it better by converting it to a codec with better 'resolution'. An audio sample full of robot voice is going to sound like the same robot voice even if you transcode it to a better quality codec, whether that is G.729, G.711u, or the latest 'HD Voice' codecs.

--Tim
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Miguel Molina | 5 Aug 22:38 2010
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Re: Codec Conversion

El 05/08/10 14:50, Tim Nelson escribió:
p { margin: 0; }
----- "michel freiha" <michofr <at> gmail.com> wrote:
>
> Dear Sir,
>
> I tried to convert ilbc to ulaw and get the same result...Bad Voice Quality
>
> Regards
>

Again, iLBC is poor quality to begin with. You can't take a poor audio sample and make it better by converting it to a codec with better 'resolution'. An audio sample full of robot voice is going to sound like the same robot voice even if you transcode it to a better quality codec, whether that is G.729, G.711u, or the latest 'HD Voice' codecs.

--Tim
This just made me remember some comment on the iax.conf sample file...

disallow=lpc10            ; Icky sound quality...  Mr. Roboto.

Cheers,
-- Ing. Miguel Molina Grupo de Tecnología Millenium Phone Center
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Jeff Brower | 5 Aug 23:40 2010

Re: Codec Conversion

Miguel-

> El 05/08/10 14:50, Tim Nelson escribió:
>> ----- "michel freiha" <michofr <at> gmail.com> wrote:
>> >
>> > Dear Sir,
>> >
>> > I tried to convert ilbc to ulaw and get the same result...Bad Voice
>> Quality
>> >
>> > Regards
>> >
>>
>> Again, iLBC is poor quality to begin with. You can't take a poor audio
>> sample and make it better by converting it to a codec with better
>> 'resolution'. An audio sample full of robot voice is going to sound
>> like the same robot voice even if you transcode it to a better quality
>> codec, whether that is G.729, G.711u, or the latest 'HD Voice' codecs.
>>
>> --Tim
> This just made me remember some comment on the iax.conf sample file...
>
> disallow=lpc10            ; Icky sound quality...  Mr. Roboto.

LPC10 is a very old codec, from early 1980s.  LPC10 doesn't do a good job with pitch detection so it tends to
have a
'robotic' sound.  With advent of MELPe, anyone needing bitrates 2400 or less should not be using LPC10.

-Jeff

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Miguel Molina | 6 Aug 00:19 2010
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Re: Codec Conversion


>> This just made me remember some comment on the iax.conf sample file...
>>
>> disallow=lpc10            ; Icky sound quality...  Mr. Roboto.
>>      
> LPC10 is a very old codec, from early 1980s.  LPC10 doesn't do a good job with pitch detection so it tends to
have a
> 'robotic' sound.  With advent of MELPe, anyone needing bitrates 2400 or less should not be using LPC10.
>
> -Jeff
>
>    
OK, on years I have working with asterisk I never have used, tested or 
even heard that old codec. I was just quoting the funny comment...

Cheers,

-- 
Ing. Miguel Molina
Grupo de Tecnología
Millenium Phone Center

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Steve Underwood | 6 Aug 02:24 2010

Re: Codec Conversion

  On 08/06/2010 05:40 AM, Jeff Brower wrote:
> Miguel-
>
>> El 05/08/10 14:50, Tim Nelson escribió:
>>> ----- "michel freiha"<michofr <at> gmail.com>  wrote:
>>>> Dear Sir,
>>>>
>>>> I tried to convert ilbc to ulaw and get the same result...Bad Voice
>>> Quality
>>>> Regards
>>>>
>>> Again, iLBC is poor quality to begin with. You can't take a poor audio
>>> sample and make it better by converting it to a codec with better
>>> 'resolution'. An audio sample full of robot voice is going to sound
>>> like the same robot voice even if you transcode it to a better quality
>>> codec, whether that is G.729, G.711u, or the latest 'HD Voice' codecs.
>>>
>>> --Tim
>> This just made me remember some comment on the iax.conf sample file...
>>
>> disallow=lpc10            ; Icky sound quality...  Mr. Roboto.
> LPC10 is a very old codec, from early 1980s.  LPC10 doesn't do a good job with pitch detection so it tends to
have a
> 'robotic' sound.  With advent of MELPe, anyone needing bitrates 2400 or less should not be using LPC10.
>
> -Jeff
MELPe is patent encumbered, so there is still a place for LPC10. LPC10 
should sound a lot better than the one in Asterisk. The Asterisk codec 
is broken.

Steve

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Jeff Brower | 6 Aug 10:43 2010

Re: Codec Conversion

Steve-

>   On 08/06/2010 05:40 AM, Jeff Brower wrote:
>> Miguel-
>>
>>> El 05/08/10 14:50, Tim Nelson escribió:
>>>> ----- "michel freiha"<michofr <at> gmail.com>  wrote:
>>>>> Dear Sir,
>>>>>
>>>>> I tried to convert ilbc to ulaw and get the same result...Bad Voice
>>>> Quality
>>>>> Regards
>>>>>
>>>> Again, iLBC is poor quality to begin with. You can't take a poor audio
>>>> sample and make it better by converting it to a codec with better
>>>> 'resolution'. An audio sample full of robot voice is going to sound
>>>> like the same robot voice even if you transcode it to a better quality
>>>> codec, whether that is G.729, G.711u, or the latest 'HD Voice' codecs.
>>>>
>>>> --Tim
>>> This just made me remember some comment on the iax.conf sample file...
>>>
>>> disallow=lpc10            ; Icky sound quality...  Mr. Roboto.
>> LPC10 is a very old codec, from early 1980s.  LPC10 doesn't do a good job with pitch detection so it tends to
have a
>> 'robotic' sound.  With advent of MELPe, anyone needing bitrates 2400 or less should not be using LPC10.
>>
>> -Jeff
> MELPe is patent encumbered,

Not if used for govt/defense purposes.  For commercial-only purposes, TI will waive royalty fees if their
chip is used
in the product.  It would have been nice if Digium had considered the many advantages of using a DSP pioneer
such as
TI before putting a Mindspeed chip on their TC400B card.

> so there is still a place for LPC10 [...]

I haven't seen an LPC10 implementation with MOS higher than 2.5.  Due to its age and expiration of patents, LPC10
might be a basis for a 2400 bps open source codec.  But enormous improvement would be needed to come close to MELPe
performance.

-Jeff

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Michael Graves | 6 Aug 14:40 2010

Re: Codec Conversion

On Fri, 6 Aug 2010 03:43:33 -0500 (CDT), Jeff Brower wrote:

<snip>

>> MELPe is patent encumbered,
>
>Not if used for govt/defense purposes.  For commercial-only purposes, TI will waive royalty fees if their
chip is used
>in the product.  It would have been nice if Digium had considered the many advantages of using a DSP pioneer
such as
>TI before putting a Mindspeed chip on their TC400B card.
>
>> so there is still a place for LPC10 [...]
>
>I haven't seen an LPC10 implementation with MOS higher than 2.5.  Due to its age and expiration of patents, LPC10
>might be a basis for a 2400 bps open source codec.  But enormous improvement would be needed to come close to MELPe
>performance.
>
>-Jeff

I wonder where David Rowe's newer CODEC2 fits into this discussion?
(http://codec2.org/)

Clearly it's not implemented anywhere yet, but it may prove yet useful
in very bandwidth constrained applications. Oh yes. It's completely
open source and should not be subject to patent issues.

Michael
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Michael Graves | 6 Aug 14:43 2010

Re: Codec Conversion

On Fri, 06 Aug 2010 07:40:44 -0500, Michael Graves wrote:

>On Fri, 6 Aug 2010 03:43:33 -0500 (CDT), Jeff Brower wrote:
>
><snip>
>
>>> MELPe is patent encumbered,
>>
>>Not if used for govt/defense purposes.  For commercial-only purposes, TI will waive royalty fees if
their chip is used
>>in the product.  It would have been nice if Digium had considered the many advantages of using a DSP pioneer
such as
>>TI before putting a Mindspeed chip on their TC400B card.
>>
>>> so there is still a place for LPC10 [...]
>>
>>I haven't seen an LPC10 implementation with MOS higher than 2.5.  Due to its age and expiration of patents, LPC10
>>might be a basis for a 2400 bps open source codec.  But enormous improvement would be needed to come close to MELPe
>>performance.
>>
>>-Jeff
>
>I wonder where David Rowe's newer CODEC2 fits into this discussion?
>(http://codec2.org/)
>
>Clearly it's not implemented anywhere yet, but it may prove yet useful
>in very bandwidth constrained applications. Oh yes. It's completely
>open source and should not be subject to patent issues.
>
>Michael

The more appropriate link should have been
http://www.rowetel.com/blog/?page_id=452

Michael
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Steve Underwood | 6 Aug 18:47 2010

Re: Codec Conversion

  On 08/06/2010 04:43 PM, Jeff Brower wrote:
> Steve-
>
>>    On 08/06/2010 05:40 AM, Jeff Brower wrote:
>>> Miguel-
>>>
>>>> El 05/08/10 14:50, Tim Nelson escribió:
>>>>> ----- "michel freiha"<michofr <at> gmail.com>   wrote:
>>>>>> Dear Sir,
>>>>>>
>>>>>> I tried to convert ilbc to ulaw and get the same result...Bad Voice
>>>>> Quality
>>>>>> Regards
>>>>>>
>>>>> Again, iLBC is poor quality to begin with. You can't take a poor audio
>>>>> sample and make it better by converting it to a codec with better
>>>>> 'resolution'. An audio sample full of robot voice is going to sound
>>>>> like the same robot voice even if you transcode it to a better quality
>>>>> codec, whether that is G.729, G.711u, or the latest 'HD Voice' codecs.
>>>>>
>>>>> --Tim
>>>> This just made me remember some comment on the iax.conf sample file...
>>>>
>>>> disallow=lpc10            ; Icky sound quality...  Mr. Roboto.
>>> LPC10 is a very old codec, from early 1980s.  LPC10 doesn't do a good job with pitch detection so it tends to
have a
>>> 'robotic' sound.  With advent of MELPe, anyone needing bitrates 2400 or less should not be using LPC10.
>>>
>>> -Jeff
>> MELPe is patent encumbered,
> Not if used for govt/defense purposes.  For commercial-only purposes, TI will waive royalty fees if their
chip is used
> in the product.  It would have been nice if Digium had considered the many advantages of using a DSP pioneer
such as
> TI before putting a Mindspeed chip on their TC400B card.

I think all the IP for MELP is now in the hands of Compandent, and TI no 
longer has the ability to waive royalties. Either way, government use 
and use with TI silicon are two niches that might work out well, and 
everything else is a problem for several more years. If you are going to 
pay royalties for a low bit rate codec, IMBE is probably a better option.

TI is a good option, but what do you have against Mindspeed? Choosing a 
good option for this kind of card is mostly about managing the patent 
licence fees. I assume Mindspeed gave Digium the best option for doing 
that, within Digium's volume constraints.
>> so there is still a place for LPC10 [...]
> I haven't seen an LPC10 implementation with MOS higher than 2.5.  Due to its age and expiration of patents, LPC10
> might be a basis for a 2400 bps open source codec.  But enormous improvement would be needed to come close to MELPe
> performance.
>
>
MELPe is definitely a compandent thing, and TI cannot waive fees for 
that. MELP and MELPe are derived from LPC10. Any attempt to improve 
LPC10 would take you down a similar road, though you would need to skirt 
around the patents.

Do you really consider MELPe to be an enormous improvement over LPC10? 
Its still pretty lousy compared to a number of options at about 5kbps, 
and RTP overheads mean the gain from going lower than 5k isn't that big. 
The main reason LPC10 and MELPe offer a low bit rate in RTP is the 
minimum packet you can pack 22.5ms frames into sanely is a 90ms one. 
90ms RTP *really* cuts the overheads, compared to the more typical 20ms 
or 30ms packets used for G.729.

As others have mentioned, David Rowe is working on a modern 2400bps 
codec. He did a burst of work some time ago, and then put it aside while 
busy with other things. He recently told me he is restarting the work, 
and he wants to get that codec into good shape before the end of this year.

Steve

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Jeff Brower | 6 Aug 21:15 2010

Re: Codec Conversion

Steve-

>>>>> El 05/08/10 14:50, Tim Nelson escribió:
>>>>>> ----- "michel freiha"<michofr <at> gmail.com>   wrote:
>>>>>>> Dear Sir,
>>>>>>>
>>>>>>> I tried to convert ilbc to ulaw and get the same result...Bad Voice
>>>>>> Quality
>>>>>>> Regards
>>>>>>>
>>>>>> Again, iLBC is poor quality to begin with. You can't take a poor audio
>>>>>> sample and make it better by converting it to a codec with better
>>>>>> 'resolution'. An audio sample full of robot voice is going to sound
>>>>>> like the same robot voice even if you transcode it to a better quality
>>>>>> codec, whether that is G.729, G.711u, or the latest 'HD Voice' codecs.
>>>>>>
>>>>>> --Tim
>>>>> This just made me remember some comment on the iax.conf sample file...
>>>>>
>>>>> disallow=lpc10            ; Icky sound quality...  Mr. Roboto.
>>>> LPC10 is a very old codec, from early 1980s.  LPC10 doesn't do a good job with pitch detection so it tends
to have
>>>> a
>>>> 'robotic' sound.  With advent of MELPe, anyone needing bitrates 2400 or less should not be using LPC10.
>>>>
>>>> -Jeff
>>> MELPe is patent encumbered,
>> Not if used for govt/defense purposes.  For commercial-only purposes, TI will waive royalty fees if
their chip is
>> used
>> in the product.  It would have been nice if Digium had considered the many advantages of using a DSP pioneer
such as
>> TI before putting a Mindspeed chip on their TC400B card.
>
> I think all the IP for MELP is now in the hands of Compandent, and TI no
> longer has the ability to waive royalties.

That is not correct.  Compandent has filed copyrights on certain files associated with a C549 chip assembly language
implementation they did under contract to NSA around 2001.  TI has patent rights on 2400 bps, TI + Microsoft
on 1200
bps, and TI + Microsoft + Thales Group on 600 bps.  Microsoft's IP came about as a result of acquiring a company
called SignalCom around 2001.  If the noise pre-processor is used, then there is some AT&T IP.  To verify
this, you
can search dsprelated.com (specifically, look for posts discussing this issue on comp.dsp), and you can
also read the
"Compandent IPR" section of the MELPe Wikipedia page
(http://en.wikipedia.org/wiki/Mixed_Excitation_Linear_Prediction).  That section was authored by
the Compandent's
founder, Oded Gottesman.  Oded is a super sharp, very hard working guy.

Compandent also claims a copyright on some C code in the file melp_syn.c (synthesis filter).  I have read discussions
by DSP experts indicating the copyrighted section of code can be implemented in alternative ways, but Oded
may say
that's not accurate.

> Either way, government use
> and use with TI silicon are two niches that might work out well, and
> everything else is a problem for several more years. If you are going to
> pay royalties for a low bit rate codec, IMBE is probably a better option.

I would disagree because IMBE source is not available.  MELPe source is available and can be downloaded online.

> TI is a good option, but what do you have against Mindspeed? Choosing a
> good option for this kind of card is mostly about managing the patent
> licence fees. I assume Mindspeed gave Digium the best option for doing
> that, within Digium's volume constraints.

My understanding in talking to Digium engineers at Globalcom and other trade shows back in 2006 is they were worried
about interfacing the TI TNET series devices over the PCI bus.  They would have needed an FPGA with some non-trivial
logic programming, so I understand their decision.  But if they had got past their FPGA "writer's block",
they could
have put one TNETV3010 chip on there, even smaller than the Mindspeed and without the heat sink, and had
twice the
channel capacity as they do now.

>>> so there is still a place for LPC10 [...]
e>> I haven't seen an LPC10 implementation with MOS higher than 2.5.  Due to its age and expiration of
patents, LPC10
>> might be a basis for a 2400 bps open source codec.  But enormous improvement would be needed to come close to MELPe
>> performance.
>>
>>
> MELPe is definitely a compandent thing, and TI cannot waive fees for
> that. MELP and MELPe are derived from LPC10. Any attempt to improve
> LPC10 would take you down a similar road, though you would need to skirt
> around the patents.

Again, not correct.  Suggest to research the many online independent sources, or contact NSA (who
initiated the
overall MELPe effort in the 1990s, in response to a need to significantly improve over LPC10) and who can
give you a
complete IP list.

> Do you really consider MELPe to be an enormous improvement over LPC10?
> Its still pretty lousy compared to a number of options at about 5kbps,
> and RTP overheads mean the gain from going lower than 5k isn't that big.
> The main reason LPC10 and MELPe offer a low bit rate in RTP is the
> minimum packet you can pack 22.5ms frames into sanely is a 90ms one.

In MOS terms, yes.  In VoIP terms, I agree it's not clear cut.  At 2400 bps, a 90 msec packet would be 27 payload
bytes.  For IP/UDP/RTP usage, that much delay could well be counterproductive.  Places where I have seen MELPe
effectively used for VoIP include applications where multiple channels are sent in one packet stream, non-Ethernet
based channels (much less overhead, for example low bandwidth satellite connections), and combining
voice and
associated data into payloads.

> 90ms RTP *really* cuts the overheads, compared to the more typical 20ms
> or 30ms packets used for G.729.
>
> As others have mentioned, David Rowe is working on a modern 2400bps
> codec. He did a burst of work some time ago, and then put it aside while
> busy with other things. He recently told me he is restarting the work,
> and he wants to get that codec into good shape before the end of this year.

Yes, it's an ambitious project!  I've read about what David's trying to do and I hope he is successful.

-Jeff

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Steve Underwood | 7 Aug 04:42 2010

Re: Codec Conversion

  On 08/07/2010 03:15 AM, Jeff Brower wrote:
> Steve-
>
>>>>>> El 05/08/10 14:50, Tim Nelson escribió:
>>>>>>> ----- "michel freiha"<michofr <at> gmail.com>    wrote:
>>>>>>>> Dear Sir,
>>>>>>>>
>>>>>>>> I tried to convert ilbc to ulaw and get the same result...Bad Voice
>>>>>>> Quality
>>>>>>>> Regards
>>>>>>>>
>>>>>>> Again, iLBC is poor quality to begin with. You can't take a poor audio
>>>>>>> sample and make it better by converting it to a codec with better
>>>>>>> 'resolution'. An audio sample full of robot voice is going to sound
>>>>>>> like the same robot voice even if you transcode it to a better quality
>>>>>>> codec, whether that is G.729, G.711u, or the latest 'HD Voice' codecs.
>>>>>>>
>>>>>>> --Tim
>>>>>> This just made me remember some comment on the iax.conf sample file...
>>>>>>
>>>>>> disallow=lpc10            ; Icky sound quality...  Mr. Roboto.
>>>>> LPC10 is a very old codec, from early 1980s.  LPC10 doesn't do a good job with pitch detection so it tends
to have
>>>>> a
>>>>> 'robotic' sound.  With advent of MELPe, anyone needing bitrates 2400 or less should not be using LPC10.
>>>>>
>>>>> -Jeff
>>>> MELPe is patent encumbered,
>>> Not if used for govt/defense purposes.  For commercial-only purposes, TI will waive royalty fees if
their chip is
>>> used
>>> in the product.  It would have been nice if Digium had considered the many advantages of using a DSP
pioneer such as
>>> TI before putting a Mindspeed chip on their TC400B card.
>> I think all the IP for MELP is now in the hands of Compandent, and TI no
>> longer has the ability to waive royalties.
> That is not correct.  Compandent has filed copyrights on certain files associated with a C549 chip
assembly language
> implementation they did under contract to NSA around 2001.  TI has patent rights on 2400 bps, TI + Microsoft
on 1200
> bps, and TI + Microsoft + Thales Group on 600 bps.  Microsoft's IP came about as a result of acquiring a company
> called SignalCom around 2001.  If the noise pre-processor is used, then there is some AT&T IP.  To verify
this, you
> can search dsprelated.com (specifically, look for posts discussing this issue on comp.dsp), and you can
also read the
> "Compandent IPR" section of the MELPe Wikipedia page
> (http://en.wikipedia.org/wiki/Mixed_Excitation_Linear_Prediction).  That section was authored
by the Compandent's
> founder, Oded Gottesman.  Oded is a super sharp, very hard working guy.
>
> Compandent also claims a copyright on some C code in the file melp_syn.c (synthesis filter).  I have read discussions
> by DSP experts indicating the copyrighted section of code can be implemented in alternative ways, but
Oded may say
> that's not accurate.
That guy is PITA. He must have driven a lot of people away from MELP by 
the way he acts. He really annoys the regulars in the comp.dsp group by 
posting astroturf questions about MELP, and giving astroturf replies 
about how fantastic it is. That probably shapes a lot of my attitude to 
MELP. :-)
>> Either way, government use
>> and use with TI silicon are two niches that might work out well, and
>> everything else is a problem for several more years. If you are going to
>> pay royalties for a low bit rate codec, IMBE is probably a better option.
> I would disagree because IMBE source is not available.  MELPe source is available and can be downloaded online.
Depends what you mean by available. IMBE is patented, just like MELP is 
patented. Licence either, and implementations are available. IMBE has 
the great benefit of being widely used for commercial and amateur low 
bit rate channels. For example, amateur radio uses IMBE - an anomaly 
which is one of the drivers for David Rowe's work on an open low bit 
rate codec. Transcoding at low bit rates is a disaster, so using a codec 
you won't need to transcode is a big plus.

>> TI is a good option, but what do you have against Mindspeed? Choosing a
>> good option for this kind of card is mostly about managing the patent
>> licence fees. I assume Mindspeed gave Digium the best option for doing
>> that, within Digium's volume constraints.
> My understanding in talking to Digium engineers at Globalcom and other trade shows back in 2006 is they
were worried
> about interfacing the TI TNET series devices over the PCI bus.  They would have needed an FPGA with some non-trivial
> logic programming, so I understand their decision.  But if they had got past their FPGA "writer's block",
they could
> have put one TNETV3010 chip on there, even smaller than the Mindspeed and without the heat sink, and had
twice the
> channel capacity as they do now.
TI have had DSP chips with a PCI interface for years, so that 
explanation doesn't make a lot of sense. Of course, these days you need 
a PCI-E interface. I'm not so sure about the status of those in DSP chips.
>> so there is still a place for LPC10 [...]

> e>>  I haven't seen an LPC10 implementation with MOS higher than 2.5.  Due to its age and expiration of
patents, LPC10
>>> might be a basis for a 2400 bps open source codec.  But enormous improvement would be needed to come close
to MELPe
>>> performance.
>>>
>>>
>> MELPe is definitely a compandent thing, and TI cannot waive fees for
>> that. MELP and MELPe are derived from LPC10. Any attempt to improve
>> LPC10 would take you down a similar road, though you would need to skirt
>> around the patents.
> Again, not correct.  Suggest to research the many online independent sources, or contact NSA (who
initiated the
> overall MELPe effort in the 1990s, in response to a need to significantly improve over LPC10) and who can
give you a
> complete IP list.
>
>> Do you really consider MELPe to be an enormous improvement over LPC10?
>> Its still pretty lousy compared to a number of options at about 5kbps,
>> and RTP overheads mean the gain from going lower than 5k isn't that big.
>> The main reason LPC10 and MELPe offer a low bit rate in RTP is the
>> minimum packet you can pack 22.5ms frames into sanely is a 90ms one.
> In MOS terms, yes.  In VoIP terms, I agree it's not clear cut.  At 2400 bps, a 90 msec packet would be 27 payload
> bytes.  For IP/UDP/RTP usage, that much delay could well be counterproductive.  Places where I have seen MELPe
> effectively used for VoIP include applications where multiple channels are sent in one packet stream, non-Ethernet
> based channels (much less overhead, for example low bandwidth satellite connections), and combining
voice and
> associated data into payloads.
>
>> 90ms RTP *really* cuts the overheads, compared to the more typical 20ms
>> or 30ms packets used for G.729.
>>
>> As others have mentioned, David Rowe is working on a modern 2400bps
>> codec. He did a burst of work some time ago, and then put it aside while
>> busy with other things. He recently told me he is restarting the work,
>> and he wants to get that codec into good shape before the end of this year.
> Yes, it's an ambitious project!  I've read about what David's trying to do and I hope he is successful.
Regards,
Steve

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Jeff Brower | 8 Aug 18:18 2010

Re: Codec Conversion

Steve-

>   On 08/07/2010 03:15 AM, Jeff Brower wrote:
>> Steve-
>>
>>>>>>> El 05/08/10 14:50, Tim Nelson escribió:
>>>>>>>> ----- "michel freiha"<michofr <at> gmail.com>    wrote:
>>>>>>>>> Dear Sir,
>>>>>>>>>
>>>>>>>>> I tried to convert ilbc to ulaw and get the same result...Bad Voice
>>>>>>>> Quality
>>>>>>>>> Regards
>>>>>>>>>
>>>>>>>> Again, iLBC is poor quality to begin with. You can't take a poor audio
>>>>>>>> sample and make it better by converting it to a codec with better
>>>>>>>> 'resolution'. An audio sample full of robot voice is going to sound
>>>>>>>> like the same robot voice even if you transcode it to a better quality
>>>>>>>> codec, whether that is G.729, G.711u, or the latest 'HD Voice' codecs.
>>>>>>>>
>>>>>>>> --Tim
>>>>>>> This just made me remember some comment on the iax.conf sample file...
>>>>>>>
>>>>>>> disallow=lpc10            ; Icky sound quality...  Mr. Roboto.
>>>>>> LPC10 is a very old codec, from early 1980s.  LPC10 doesn't do a good job with pitch detection so it
tends to
>>>>>> have
>>>>>> a
>>>>>> 'robotic' sound.  With advent of MELPe, anyone needing bitrates 2400 or less should not be using LPC10.
>>>>>>
>>>>>> -Jeff
>>>>> MELPe is patent encumbered,
>>>> Not if used for govt/defense purposes.  For commercial-only purposes, TI will waive royalty fees if
their chip is
>>>> used
>>>> in the product.  It would have been nice if Digium had considered the many advantages of using a DSP
pioneer such
>>>> as
>>>> TI before putting a Mindspeed chip on their TC400B card.
>>> I think all the IP for MELP is now in the hands of Compandent, and TI no
>>> longer has the ability to waive royalties.
>> That is not correct.  Compandent has filed copyrights on certain files associated with a C549 chip
assembly language
>> implementation they did under contract to NSA around 2001.  TI has patent rights on 2400 bps, TI +
Microsoft on 1200
>> bps, and TI + Microsoft + Thales Group on 600 bps.  Microsoft's IP came about as a result of acquiring a company
>> called SignalCom around 2001.  If the noise pre-processor is used, then there is some AT&T IP.  To verify
this, you
>> can search dsprelated.com (specifically, look for posts discussing this issue on comp.dsp), and you
can also read
>> the
>> "Compandent IPR" section of the MELPe Wikipedia page
>> (http://en.wikipedia.org/wiki/Mixed_Excitation_Linear_Prediction).  That section was authored
by the Compandent's
>> founder, Oded Gottesman.  Oded is a super sharp, very hard working guy.
>>
>> Compandent also claims a copyright on some C code in the file melp_syn.c (synthesis filter).  I have read
>> discussions
>> by DSP experts indicating the copyrighted section of code can be implemented in alternative ways, but
Oded may say
>> that's not accurate.
> That guy is PITA. He must have driven a lot of people away from MELP by
> the way he acts. He really annoys the regulars in the comp.dsp group by
> posting astroturf questions about MELP, and giving astroturf replies
> about how fantastic it is. That probably shapes a lot of my attitude to
> MELP. :-)
>>> Either way, government use
>>> and use with TI silicon are two niches that might work out well, and
>>> everything else is a problem for several more years. If you are going to
>>> pay royalties for a low bit rate codec, IMBE is probably a better option.
>> I would disagree because IMBE source is not available.  MELPe source is available and can be downloaded online.
> Depends what you mean by available. IMBE is patented, just like MELP is
> patented. Licence either, and implementations are available.

I meant that MELPe C source code is available for non-commercial purposes (academic, R&D, bug fixes and
other source
level improvements) without payment and without signing a license agreement with a corporation (such as
Digital Voice
with IMBE).

> IMBE has
> the great benefit of being widely used for commercial and amateur low
> bit rate channels. For example, amateur radio uses IMBE - an anomaly
> which is one of the drivers for David Rowe's work on an open low bit
> rate codec. Transcoding at low bit rates is a disaster, so using a codec
> you won't need to transcode is a big plus.

Yes all good points.  IMBE and AMBE have surely been successful, testaments to the Digital Voice guys and their
pioneering work in the LBR codec area.

>>> TI is a good option, but what do you have against Mindspeed? Choosing a
>>> good option for this kind of card is mostly about managing the patent
>>> licence fees. I assume Mindspeed gave Digium the best option for doing
>>> that, within Digium's volume constraints.
>> My understanding in talking to Digium engineers at Globalcom and other trade shows back in 2006 is they
were worried
>> about interfacing the TI TNET series devices over the PCI bus.  They would have needed an FPGA with some non-trivial
>> logic programming, so I understand their decision.  But if they had got past their FPGA "writer's block",
they could
>> have put one TNETV3010 chip on there, even smaller than the Mindspeed and without the heat sink, and had
twice the
>> channel capacity as they do now.
> TI have had DSP chips with a PCI interface for years, so that
> explanation doesn't make a lot of sense. Of course, these days you need
> a PCI-E interface. I'm not so sure about the status of those in DSP chips.

Good insight, but there's another layer of subtlety.  The TNETV3010 was the most "channel dense" VoIP chip
that TI had
during the 2002-2008 time frame (192 chan, 16x16 mm package).  Underneath the hood, the chip is a 6-core C55x device,
but doesn't have a PCI bus interface like so many of their other DSPs.

-Jeff

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michel freiha | 9 Aug 12:30 2010
Picon

Re: Codec Conversion

Hello Miguel molina,

I did what you asked, but still the voice is too bad

Regards

On Thu, Aug 5, 2010 at 11:38 PM, Miguel Molina <mmolina <at> millenium.com.co> wrote:
El 05/08/10 14:50, Tim Nelson escribió:
----- "michel freiha" <michofr <at> gmail.com> wrote:
>
> Dear Sir,
>
> I tried to convert ilbc to ulaw and get the same result...Bad Voice Quality
>
> Regards
>

Again, iLBC is poor quality to begin with. You can't take a poor audio sample and make it better by converting it to a codec with better 'resolution'. An audio sample full of robot voice is going to sound like the same robot voice even if you transcode it to a better quality codec, whether that is G.729, G.711u, or the latest 'HD Voice' codecs.

--Tim
This just made me remember some comment on the iax.conf sample file...

disallow=lpc10            ; Icky sound quality...  Mr. Roboto.

Cheers,
-- Ing. Miguel Molina Grupo de Tecnología Millenium Phone Center

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Miguel Molina | 9 Aug 16:06 2010
Picon

Re: Codec Conversion

El 09/08/10 05:30, michel freiha escribió:
Hello Miguel molina,

I did what you asked, but still the voice is too bad

Regards

On Thu, Aug 5, 2010 at 11:38 PM, Miguel Molina <mmolina <at> millenium.com.co> wrote:
El 05/08/10 14:50, Tim Nelson escribió:
----- "michel freiha" <michofr <at> gmail.com> wrote:
>
> Dear Sir,
>
> I tried to convert ilbc to ulaw and get the same result...Bad Voice Quality
>
> Regards
>

Again, iLBC is poor quality to begin with. You can't take a poor audio sample and make it better by converting it to a codec with better 'resolution'. An audio sample full of robot voice is going to sound like the same robot voice even if you transcode it to a better quality codec, whether that is G.729, G.711u, or the latest 'HD Voice' codecs.

--Tim
This just made me remember some comment on the iax.conf sample file...

disallow=lpc10            ; Icky sound quality...  Mr. Roboto.

Cheers,
-- Ing. Miguel Molina Grupo de Tecnología Millenium Phone Center

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Hi,

I didn't ask nothing... but as Tim said you are encouraged to change the iLBC codec to other (could be GSM) and do some tests. Play with several codecs and see which one fits your needs or whether this is not a codec or transcoding issue.

Regards,
-- Ing. Miguel Molina Grupo de Tecnología Millenium Phone Center
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Jeff Brower | 5 Aug 22:50 2010

Re: Codec Conversion

Michel-

> I tried to convert ilbc to ulaw and get the same
> result...Bad Voice Quality

I think you have to be more specific when you say "bad voice quality".  Like what?  Worse than a cellphone call?  Gaps
of audio missing?  Robotic or "cyborg" sound?  Static?  A background tone or buzzing?

iLBC isn't any worse voice quality than other LBR codecs (GSM-AMR, EVRC, etc).  If you want land-line
quality and what
you're hearing is cellphone quality, then you're asking too much.  Otherwise, suggest to be specific and
detailed in
describing your problem.

-Jeff

> On Thu, Aug 5, 2010 at 4:13 PM, Tim Nelson <tnelson <at> rockbochs.com> wrote:
>
>> ----- "michel freiha" <michofr <at> gmail.com> wrote:
>> >
>> > Dear All,
>> >
>> > i would like to ask please if someone tried to make a codec conversion
>> from ilbc to g729, because i did that but the voice quality was too bad and
>> a lot of disconnection..
>> >
>> > Can i get your feedback regarding this issue please?
>> >
>> > regards
>>
>> I can't comment on your 'disconnection' as you don't say if that means the
>> call is disconnected or you're getting stuttered audio. Regardless, iLBC has
>> one of the lowest bitrates of the available codecs and as such the voice
>> quality is not spectacular to begin with. Take 'not so good' audio and try
>> to convert it to another audio format, and the deficiencies can be
>> exacerbated.
>>
>> --Tim

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Brian C. Fertig | 17 Jan 18:54 2005

RE: Codec conversion

In your SIP.CONF you need to tell * what codecs to use.  

 

sip.conf

[broadvoice]

disallow=all

allow=ulaw

 

[phone]

disallow=all

allow=g729

 

Then in your extensions.conf you just have it dial as usual.

 

 

 

.o-------------------------------------------------------o.

Brian Fertig

Network Engineer

Planet Telecom, Inc.

Tampa, FL Office

 

From: asterisk-users-bounces <at> lists.digium.com [mailto:asterisk-users-bounces <at> lists.digium.com] On Behalf Of Helder Rogério [MICROREDE]
Sent: Monday, January 17, 2005 11:34 AM
To: Asterisk Users Mailing List - Non-Commercial Discussion
Subject: [Asterisk-Users] Codec conversion

 

Hi!

 

Is there any way to receive in * server a call from a Terminal adapter in G.723/G.729 and then convert it to G.711?

 

I'm wondering this because I can only place all thru Broadvoice in G.711 but most of customers have ADSL connection with 128k upstream, so the result is that they can hear in excellent conditions but can't be heard very well the sound is all choppy. even directly to broadvoice thru Xten sip client.

 

So the idea was to act as "proxy" and "codec converter" so that the communication coming out their router is the smaller it can get. I've mentioned G729 or G.723 becuase their routers have it, (Draytek 2600V).

 

Thanks in advance for your suggestions

Helder Rogerio

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Gmane