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Discussion Groups | Speech Coding | Why high pass filtering and down scaling in pre processing
Technical discussions related to Speech Coding (all itu and other vocoders, ACELP, CELP, AMR, etc)
Why high pass filtering and down scaling in pre processing - subrata chatterjee - Apr 25 14:52:00 2002
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hi friends, In AMR speech codec why do we need to use high pass filtering and down scaling in pre processing??? Again the technique of down scalling is not clear to me....So please anyone help me by answering the above queries in detail. Thanks in advance Subrata |
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Re: Why high pass filtering and down scaling in pre processing - Bhanu Prakash - Apr 26 4:32:00 2002
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Re: Why high pass filtering and down scaling in pre processing - Sameer Kibey - Apr 27 4:42:00 2002
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Hi all! as far as the use of high pass filter in preprocessing is concerned,the reasoning of removal of the 50/60 Hz hum is indeed agreeable. another use of the high pass filter could be removal of an unnecessary DC offset present in the signal. now, my question : is the addition of such a DC component in speech posssible? if yes, what is the cause/source of this DC offset? Sameer. --- Bhanu Prakash <> wrote: > Hi Subrata, > The answers for ur questions are: > 1.The high pass filtering in any speech codec is to > filter out > flicker noise(1/f) and also to filter interference > of 50/60 hz hum. > 2.Signal down scaling is to minimise handling of > overflow conditions > down the path of processing in case of fixed point > operations. > This is compensated by signal upscaling at the > decoder. > > I think i have answered your questions.If any one > has any other answers > i would like to hear. > > Best Regards, > Prakash. __________________________________________________ |
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Re: Why high pass filtering and down scaling in pre processing - T Prasanthan - Apr 29 12:48:00 2002
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Sameer Kibey wrote: > Hi all! > > as far as the use of high pass filter in preprocessing > is concerned,the reasoning of removal of the 50/60 Hz > hum is indeed agreeable. > another use of the high pass filter could be removal > of an unnecessary DC offset present in the signal. > now, my question : is the addition of such a DC > component in speech posssible? if yes, what is the > cause/source of this DC offset? Such DC offsets can come from ADC (Analog to Digital Converters). They are basically analog devices, whose properties might change depending on various factors. I have observed many times the digital speech signal contained some DC values (non zero mean), immediately after the ADC, which is not good for many of the speech codecs. The problem can be solved using a very inexpensive high pass filter. > > Sameer. > > --- Bhanu Prakash <> wrote: > > Hi Subrata, > > The answers for ur questions are: > > 1.The high pass filtering in any speech codec is to > > filter out > > flicker noise(1/f) and also to filter interference > > of 50/60 hz hum. > > 2.Signal down scaling is to minimise handling of > > overflow conditions > > down the path of processing in case of fixed point > > operations. > > This is compensated by signal upscaling at the > > decoder. > > > > I think i have answered your questions.If any one > > has any other answers > > i would like to hear. > > > > Best Regards, > > Prakash. > > > > __________________________________________________ > > _____________________________________ |
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Re: Why high pass filtering and down scaling in pre processing - krishnamurthy vaidyanathan - Apr 30 2:05:00 2002
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Is it possible that a DC offset be added at the digitizing stage - say unmatched A/D s ? Poochi --- Sameer Kibey <> wrote: > Hi all! > > as far as the use of high pass filter in > preprocessing > is concerned,the reasoning of removal of the 50/60 > Hz > hum is indeed agreeable. > another use of the high pass filter could be removal > of an unnecessary DC offset present in the signal. > now, my question : is the addition of such a DC > component in speech posssible? if yes, what is the > cause/source of this DC offset? > > Sameer. > > --- Bhanu Prakash <> > wrote: > > Hi Subrata, > > The answers for ur questions are: > > 1.The high pass filtering in any speech codec is > to > > filter out > > flicker noise(1/f) and also to filter interference > > of 50/60 hz hum. > > 2.Signal down scaling is to minimise handling of > > overflow conditions > > down the path of processing in case of fixed point > > operations. > > This is compensated by signal upscaling at the > > decoder. > > > > I think i have answered your questions.If any one > > has any other answers > > i would like to hear. > > > > Best Regards, > > Prakash. > > __________________________________________________ > > ------------------------ Yahoo! Groups Sponsor > > _____________________________________ ===== Great God, I ask thee for no meaner pelf Than that I may not disappoint myself -Thoreau __________________________________________________ |
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