[Freeswitch-dev] Audio hard-limiting vs. switch_normalize_to_16bit (was: Re: Codes I don't understand)

[Anthony Minessale]

we used to use libresample which generated a lot of samples over the limit
and that / 2 supressed the static it was causing.
We use the speex resampler now and it's much better, so i took the / 2 out
in tree.


On Tue, Apr 7, 2009 at 10:02 AM, Anthony Minessale <
anthony.minessale at gmail.com> wrote:

> if everyone has such good ideas on how to improve it, I can't wait to see
> the patch.
>
>
>
> On Tue, Apr 7, 2009 at 9:42 AM, seven du <seven at idapted.com> wrote:
>
>> And, actually the value to be normalized is 32bit and which generally
>> is a sum of two 16bit values( read and write ), so it's probably easy
>> to exceed 32767 if both end speaking at the same time.
>>
>> On Apr 7, 2009, at 12:15 PM, Nic Bellamy wrote:
>>
>> > Anthony Minessale wrote:
>> >> 2) the macro is designed to fight clipping:
>> >>    When a sample exceeds the max size of the datatype we set it to
>> >> the max value then cut the volume in half of that sample so it does
>> >> not make too much noise.  if we divide everything by 2 then all the
>> >> volume would be reduced even on samples that fell inside the proper
>> >> range.
>> > Hi Anthony, all,
>> >    this is, in my opinion, actually going to give you far far uglier
>> > audio artefacts than simply hard limiting the samples. Rather than try
>> > and describe the resulting distortion, it's easier to just listen to
>> > it
>> > in action...
>> >
>> > Each of the following files is about 100kb.
>> >
>> > Original file (extracted from
>> > freeswitch-sounds-en-us-callie-8000-1.0.7.tar.gz):
>> > http://www.vadacom.co.nz/engineering/ivr-sample_submenu.wav
>> >
>> >
>> > After 30dB gain and hard limiting samples to between -32768 and 32767:
>> > http://www.vadacom.co.nz/engineering/ivr-sample_submenu-
>> > hardlimited.wav
>> >
>> >
>> > After 30dB gain and switch_normalize_to_16bit():
>> >
>> http://www.vadacom.co.nz/engineering/ivr-sample_submenu-switch_normalize_to_16bit.wav
>> >
>> >
>> > Cheers,
>> >    Nic.
>> >
>> > --
>> > Nic Bellamy,
>> > Head Of Engineering, Vadacom Ltd - http://www.vadacom.co.nz/
>> >
>> >
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>>
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>
>
>
> --
> Anthony Minessale II
>
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-- 
Anthony Minessale II

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