Pre-emphasis in the frequency domain...

It is common practice in speech research to apply a pre-emphasis
filter before FFT in order to boost high frequency by 6dB/octave. I
was told that multiplying the spectrum points by its frequency would
yield the same 6dB/octave effect on the spectrum. The only mention of
such method I could locate was in (Oppenheim 1970):
    "If S(w) represents the spectral section to be displayed, the high
frequency emphasis is accomplished by multiplying S(w) by a function
L(w), which is constant to some frequency and thereafter increases
linearly with a specified slope"

Now, my understanding of DSP is minimal but I can learn fast if
directed well :) So if you have any information related to this,
please post back...

Any and all help will be appreciated...

@ARTICLE{Oppenheim1970,
  author = {A. Oppenheim},
  title = {Speech spectrograms using the fast Fourier Transform},
  journal = {IEEE Spectrum},
  year = {1970},
  volume = {7},
  number = {8},
  pages = {57-62},
  month = {Aug.},
}

jandouh@yahoo.com (Mohamed) wrote in message news:<e599c748.0410062345.45213acc@posting.google.com>...
> It is common practice in speech research to apply a pre-emphasis
> filter before FFT in order to boost high frequency by 6dB/octave. I
> was told that multiplying the spectrum points by its frequency would
> yield the same 6dB/octave effect on the spectrum. The only mention of
> such method I could locate was in (Oppenheim 1970):
>     "If S(w) represents the spectral section to be displayed, the high
> frequency emphasis is accomplished by multiplying S(w) by a function
> L(w), which is constant to some frequency and thereafter increases
> linearly with a specified slope"


Also see B. Gold & N. Morgan, "Speech and Audio Signal Processing:
Processing and Perception of Speech and Music"

The type of speech feature extraction advocated by Morgan and
colleagues at UCal Berkeley / ICSI is called Perceptual Linear
Prediction (PLP).  On page 299 of the text mentioned above, Morgan
pre-emphasizes the smoothed power spectrum in the process of
performing feature extraction.  (Figure 22.4 "LPC vs. PLP")  If you
need more details, let me know.

- Jesse

hansenj at ele dot uri dot edu

jandouh@yahoo.com (Mohamed) wrote in message news:<e599c748.0410062345.45213acc@posting.google.com>...
> It is common practice in speech research to apply a pre-emphasis
> filter before FFT in order to boost high frequency by 6dB/octave. I
> was told that multiplying the spectrum points by its frequency would
> yield the same 6dB/octave effect on the spectrum. The only mention of
> such method I could locate was in (Oppenheim 1970):
>     "If S(w) represents the spectral section to be displayed, the high
> frequency emphasis is accomplished by multiplying S(w) by a function
> L(w), which is constant to some frequency and thereafter increases
> linearly with a specified slope"

Also see B. Gold & N. Morgan, "Speech and Audio Signal Processing:
Processing and Perception of Speech and Music"

The type of speech feature extraction advocated by Morgan and
colleagues at UCal Berkeley / ICSI is called Perceptual Linear
Prediction (PLP).  On page 299 of the text mentioned above, Morgan
pre-emphasizes the smoothed power spectrum in the process of
performing feature extraction.  (Figure 22.4 "LPC vs. PLP")  If you
need more details, let me know.

- Jesse

hansenj at ele dot uri dot edu

hansenj@ele.uri.edu (Jesse Hansen) wrote in message news:<21d5c5c7.0410070955.b827dfc@posting.google.com>...

> 
> Also see B. Gold & N. Morgan, "Speech and Audio Signal Processing:
> Processing and Perception of Speech and Music"
> 
> The type of speech feature extraction advocated by Morgan and
> colleagues at UCal Berkeley / ICSI is called Perceptual Linear
> Prediction (PLP).  On page 299 of the text mentioned above, Morgan
> pre-emphasizes the smoothed power spectrum in the process of
> performing feature extraction.  (Figure 22.4 "LPC vs. PLP")  If you
> need more details, let me know.
> 
> - Jesse
> 
> hansenj at ele dot uri dot edu


Thanks for the info. I am waiting on the book from our uni, library. I
will post back after reading.