Re: converting unsigned short sample to signed short sample

Thanks for replying.
actually 2^15 in decimal is the same as 0x8000 in hex.
the idea is clear for me that i should scale down each unsigned sample by 0x8000 for becoming signed. I hope that will work correctly as input raw samples to Speex codec. do you think so ?

Regards,
Mash'al



________________________________
 From: Steve Checkoway <[email protected]>
To: Mashal al-shboul <[email protected]> 
Cc: Arthurc <[email protected]>; "[email protected]" <[email protected]> 
Sent: Wednesday, March 14, 2012 9:01 AM
Subject: Re: [Speex-dev] converting unsigned short sample to signed short sample
 

I don't understand why you're subtracting 2^15 - 1.  Assuming you really do have unsigned samples (which is very odd) that have 0x8000 as the mid point of the range, then you need to subtract 0x8000, as I believe I pointed out already.

By mid point, I mean if you have a pure tone (i.e., a sine wave) that has unsigned range 0 to 0xffff, then the mid point is 0x8000. The mid point should be translated to zero. 

If your samples are represented some other way, you have to tell us.


-- 
Stephen Checkoway



On Mar 13, 2012, at 23:28, Mashal al-shboul <[email protected]> wrote:


Thanks a lot for replying,
>The question now is , after subtracting 32767 from each unsigned sample, will the new signed samples represent the same original voice ? 
>
>     For explanation, assume "Hi" is said in 8000 unsigned sample ,if i subtract 32767 from each sample and play the resulting 8000 sample as signed PCM samples,will they be "Hi" ?!
>
>
>Forgive me about my questions , but it's important for me and i am new to the stuff
>
>Best Regards,
>Mash'al
>
>
>
>
>________________________________
> From: Arthurc <[email protected]>
>To: Mashal al-shboul <[email protected]> 
>Sent: Wednesday, March 14, 2012 5:58 AM
>Subject: Re: [Speex-dev] converting unsigned short sample to signed short sample
> 
>
>I assumed that you have unsigned input from your sound card / codec, etc.
>Actually, it is unlikely in today's hardware platform for audio application.
>
>
>If that is really the case, you can just do..
>
>
>short output = ((long) input) - 32767
>
>
>Well, maybe it is possible to do some bit manipulation to achieve the same thing.
>
>
>Regards
>Arthur 
>
>On 2012年3月14日, at 上午11:21, Mashal al-shboul <[email protected]> wrote:
>
>
>    Hi All,
>>I would like to get your help in my problem,
>>
>>
>>we know that Speex codec takes samples of type short (signed), range:-2^15 to2^15 -1 , my problem is that i have samples of type 
>>
>>unsigned short ,range: 0 to 2^16 -1. so, what should i do in order to apply speex on my unsigned samples ?.
>>
>>     There is  a proposed solution to subtract 2^15-1 from each unsigned short to get it signed short, my question: is this method safe in keeping the samples meaningful for speex's processing algorithms?. 
>>
>>i hope i receive help from you. Thanks in advance
>>
>>
>>Regards,
>>Mash'al
>>
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>
>
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