hy all,

1. I want to ask, how to find the preemp coefficient 15/16=0.98..??

2. why in LPC anlysis we using FIR & in LPC synthesis we use IIR

filter? what is the reason?

thanks,,

# preemphasis filter, FIR, IIR

Started by ●August 7, 2008

Reply by ●August 8, 20082008-08-08

Hi,

answer to query 2:

Recall the LP formulation

s^(n) = sum(ak. s(n-k)).

The error signal is

e(n) = s(n) - s^(n)

Or,

E(z) = S(z) A(z), where A(z) is the all-zero or FIR filter or inverse filter.

The above equation is LP analysis equation, where we derive the

error signal form the speech signal.

The synthesis equation is

S(z) = E(z) H(z), where H(z) = 1/A(z), is an all-pole filter, also

called as the synthesis filter or LP filter .

Ans. to query 1:

The idea of preemphasis during LP analysis is to reduce the spectral dynamic

range. In particular, the lower frequencies have significant energy, and dictate the

shape of spectral envelope as estimated by LP analysis. To reduce this effect,

use x(n) = s(n) - a.s(n-1). Use a close to 1, say 0.99.

This is equivalent to a high pass filtering, though not with a sharp cutoff.

This somewhat deemphasizes the low frequency components and ensures that

the estimate of the spectral envelope, as obtained by LP analysis, is not unduly

influenced by the large spectral magnitude in low-frequency range.

-Guru

--- On Thu, 8/7/08, phitenk wrote:

From: phitenk

Subject: [speechcoding] preemphasis filter, FIR, IIR

To: s...

Date: Thursday, August 7, 2008, 6:55 PM

hy all,

1. I want to ask, how to find the preemp coefficient 15/16=0.98.. ??

2. why in LPC anlysis we using FIR & in LPC synthesis we use IIR

filter? what is the reason?

thanks,,

answer to query 2:

Recall the LP formulation

s^(n) = sum(ak. s(n-k)).

The error signal is

e(n) = s(n) - s^(n)

Or,

E(z) = S(z) A(z), where A(z) is the all-zero or FIR filter or inverse filter.

The above equation is LP analysis equation, where we derive the

error signal form the speech signal.

The synthesis equation is

S(z) = E(z) H(z), where H(z) = 1/A(z), is an all-pole filter, also

called as the synthesis filter or LP filter .

Ans. to query 1:

The idea of preemphasis during LP analysis is to reduce the spectral dynamic

range. In particular, the lower frequencies have significant energy, and dictate the

shape of spectral envelope as estimated by LP analysis. To reduce this effect,

use x(n) = s(n) - a.s(n-1). Use a close to 1, say 0.99.

This is equivalent to a high pass filtering, though not with a sharp cutoff.

This somewhat deemphasizes the low frequency components and ensures that

the estimate of the spectral envelope, as obtained by LP analysis, is not unduly

influenced by the large spectral magnitude in low-frequency range.

-Guru

--- On Thu, 8/7/08, phitenk wrote:

From: phitenk

Subject: [speechcoding] preemphasis filter, FIR, IIR

To: s...

Date: Thursday, August 7, 2008, 6:55 PM

hy all,

1. I want to ask, how to find the preemp coefficient 15/16=0.98.. ??

2. why in LPC anlysis we using FIR & in LPC synthesis we use IIR

filter? what is the reason?

thanks,,