I made additional tests, and... I'm not sure any more. So, I removed
the statement about bad precision. This needs a lab environment with
predictable network and known CPU load on the host machine.

Does anyone know any tools that would automatically detect sound
distortions in WAV files and also find the shifts because of slipping
clock or lost frames?  Up to now, the only tool I could find is
visually comparing the waves in Audacity.



On Sun, Apr 5, 2015 at 2:37 AM, Stanislav Sinyagin <ssinyagin@gmail.com> wrote:

> here we go:
> https://txlab.wordpress.com/2015/04/05/testing-rtp-clock-precision-on-a-virtual-machine/
>
>
>
> On Sat, Apr 4, 2015 at 4:26 PM, Stanislav Sinyagin <ssinyagin@gmail.com> wrote:
>> On Sat, Apr 4, 2015 at 1:03 PM, Regis M <regis.freeswitch.org@tornad.net> wrote:
>>> How do you check wavs together in audacity ?
>>
>> you just open two WAV files, align their starting position, and
>> visually check the waves. If there's a problem, you would see that
>> after few seconds, the waves are not aligned any more.
>>
>>> Can you send me 2 samples wav (send... and recorded) so I could see the 20ms
>>> diff that you exposed...
>>>
>>> Is there a way to automate the result checking, so it could help to monitor
>>> itsp quality
>>
>> Here
>> https://github.com/openpreserve/scape-xcorrsound/issues/17
>> this is a link to a tool which compares two sound files at the wave
>> level. You can also see the sound samples in the ticket.
>> The problem is, that currently this tool does not detect such slipping frames.
>>
>> I will also write a detailed article with examples, during the weekend.
>>
>>
>>
>>
>>
>>>
>>>
>>> 2015-04-04 12:53 GMT+02:00 Stanislav Sinyagin <ssinyagin@gmail.com>:
>>>>
>>>> Important is to send the media through two independent carriers - then you
>>>> can be sure that your clock is compared against a high quality one.
>>>>
>>>> On Apr 4, 2015 12:46 PM, "Regis M" <regis.freeswitch.org@tornad.net>
>>>> wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> It's a very interresting test and conclusion.
>>>>>
>>>>> I will try to build a similar environnement on my freeswitch to check
>>>>> some system :)
>>>>>
>>>>> thanks
>>>>>
>>>>>
>>>>>
>>>>> 2015-04-04 2:16 GMT+02:00 Stanislav Sinyagin <ssinyagin@gmail.com>:
>>>>>>
>>>>>> hi,
>>>>>>
>>>>>> Here are some test results which might be interesting:
>>>>>>
>>>>>> I've set up a test FreeSWITCH server at digitalocean (they use KVM),
>>>>>> and originated test calls to some ITSP accounts. Each call played a
>>>>>> test sound file (voice samples from ITU:
>>>>>> http://www.itu.int/net/itu-t/sigdb/genaudio/AudioForm-g.aspx?val=1000050
>>>>>> ), and on the receiving end another FreeSWITCH server was recording
>>>>>> the received session. The receiving server was on a XEN VM. Both
>>>>>> servers talked G711 to their corresponding ITSP accounts.
>>>>>>
>>>>>> Then I compared the source audio and received audio in Audacity editor.
>>>>>>
>>>>>> The tests showed that the received voice wave shifts 20ms from the
>>>>>> original sound every few seconds, randomly back and forward. This
>>>>>> skewing was always present, regardless of ITSP and time of day.
>>>>>>
>>>>>> Then I moved the sending server to a XEN VM, and the waves appeared
>>>>>> almost perfectly synchronized (there was a 5ms skew in one test, and I
>>>>>> guess it's related to transcoding buffer, as the sound was obviously
>>>>>> transcoded).
>>>>>>
>>>>>> The effect was always visible with a 30-second sample, and I also made
>>>>>> additional tests with 2-minute samples.
>>>>>>
>>>>>> It would also be interesting to test this from a VmWare VM. If someone
>>>>>> wants to run such a test, feel free to contact me directly.
>>>>>>
>>>>>>
>>>>>> cheers,
>>>>>> stan
>>>>>>
>>>>>>
>>>>>> _________________________________________________________________________
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>>>>>>
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>>>>>
>>>>>
>>>>>
>>>>> _________________________________________________________________________
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>>>>>
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>>>>
>>>> _________________________________________________________________________
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>>>> http://www.freeswitchsolutions.com
>>>>
>>>> Official FreeSWITCH Sites
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>>>
>>>
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>>> http://www.freeswitchsolutions.com
>>>
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