[Freeswitch-users] echo cancelation

[Sergey Safarov]

Missed link http://www.rowetel.com/blog/?page_id=454

On Sat, Apr 18, 2015 at 2:55 PM, Sergey Safarov <s.safarov at gmail.com> wrote:

> According "Installing OSLEC with DAHDI" - DAHDI may use OSLEC. But I cant
> find DAHDI requirements to compile and use OSLEC. In other words OSLEC may
> be used without DAHDI.
>
> On Sat, Apr 18, 2015 at 2:25 PM, Nandy Dagondon <nandy1925 at gmail.com>
> wrote:
>
>>
>> OSLEC works with FreeTDM DAHDI-mode.
>>
>> On Sat, Apr 18, 2015 at 7:13 PM, Sergey Safarov <s.safarov at gmail.com>
>> wrote:
>>
>>> How would you expect to use echo cancellation in FS?
>>> I thinking it can be used like t38_gateway application (audio to image
>>> converter). In echo canceler application audio with echo converted to audio
>>> without echo.
>>>
>>> > On the one hand SpanDSP library compiled with FS and contains
>>> > functions for echo canceler libs/spandsp/src/echo.c
>>> Not really. Look carefully at those routines.
>>> In source
>>>  * echo.c - An echo cancellor, suitable for electrical and acoustic
>>>  *          cancellation. This code does not currently comply with
>>>  *          any relevant standards (e.g. G.164/5/7/8). One day....
>>> And other 70 string of following comments describe file as echo canceler
>>> Also in echo_can_update()
>>> at string 429
>>> clean_rx = rx - echo_value;
>>>
>>> at string 569
>>>     if ((ec->adaption_mode & ECHO_CAN_USE_NLP))
>>>     {
>>>         /* Non-linear processor - a fancy way to say "zap small signals,
>>> to avoid
>>>            residual echo due to (uLaw/ALaw) non-linearity in the
>>> channel.". */
>>>
>>> Look in echo.h comments ....
>>>
>>> in the echo_tests.c
>>> The echo cancellation tests test the echo cancellor against the G.168
>>> spec.
>>>
>>> At http://www.rowetel.com/blog/?page_id=454 I read
>>> spandsp : A subset of spandsp to support testing and development of
>>> Oslec. The echo canceller and G168 test suite source code live in here.
>>>
>>> I thinking it really echo canceler functions.
>>>
>>> SpanDSP does NOT contain OSLEC. OSLEC has its origins in the work in
>>> progress echo canceller in SpanDSP.
>>> If it two different product then echo canceler may be realized by
>>>
>>>    1. SpanDSP library
>>>    2. Oslec kernel driver
>>>
>>> I has find relation In source files between OSLEC kernel driver
>>> (drivers/staging/echo) and SpanDSP functions:
>>> oslec_create(int len, int adaption_mode) - echo_can_init(int len, int
>>> adaption_mode)
>>> oslec_adaption_mode(struct oslec_state *ec, int adaption_mode) -
>>> oslec_update(struct oslec_state *ec, int16_t tx, int16_t rx)
>>> - echo_can_update(echo_can_state_t *ec, int16_t tx, int16_t rx)
>>> oslec_hpf_tx(struct oslec_state *ec, int16_t tx)
>>> - echo_can_hpf_tx(echo_can_state_t *ec, int16_t tx)
>>>
>>> And FS may use two echo canceler engines (SpanSDP or OSLEC kernel
>>> driver). What is prevent to do it?
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> On Sat, Apr 18, 2015 at 12:39 PM, Steve Underwood <steveu at coppice.org>
>>> wrote:
>>>
>>>> On 04/18/2015 02:40 PM, Sergey Safarov wrote:
>>>> > Could you help me understand that prevents the use echo cancellation
>>>> in FS
>>>> How would you expect to use echo cancellation in FS?
>>>> > On the one hand SpanDSP library compiled with FS and contains
>>>> > functions for echo canceler libs/spandsp/src/echo.c
>>>> Not really. Look carefully at those routines.
>>>> > On the other hand FS does not contain applications of echo canceler.
>>>> Correct.
>>>> > Also, I found the discussion in which states GPL is not compatible
>>>> > with the MPL1.1 and it prevent use Oslec (SpanDSP is uses Oslec).
>>>> SpanDSP does NOT contain OSLEC. OSLEC has its origins in the work in
>>>> progress echo canceller in SpanDSP.
>>>>
>>>> Regards,
>>>> Steve
>>>>
>>>>
>>>>
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>>>
>>>
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>>
>>
>> _________________________________________________________________________
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>
>
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