Newsgroups: comp.speech
Path: pavo.csi.cam.ac.uk!warwick!uknet!pipex!sunic!EU.net!sun4nl!relay.philips.nl!prle!atheris!toma
From: toma@prl.philips.nl (Toma Cristian)
Subject: help - info request
Message-ID: <toma.760867736@atheris>
Sender: news@prl.philips.nl (USENET News System)
Organization: Philips Research Laboratories Eindhoven, Netherlands
Date: Thu, 10 Feb 1994 08:08:56 GMT
Lines: 46

I am posting this for a friend. Please direct your answers to his 
e-mail address (see below)

=================================================================
Hi everybody,

I work on a 2400 LPC pitch excited vocoder, around a TMS320C25.
I will bother you with two questions. Maybe you will find them 
annoying, but my future depends on their answers :-)

1. I use a Levinson-Durbin algorithm for reflexion coeficients 
extraction and AMDF for pitch extraction. Things go quite
well but I have some problems with the voiced/unvoiced decision.
In 'The Government Standard Linear Predictive Coding Algorithm:
LPC-10' by Thomas E. Tremain (as in other papers) I can read:
"The voicing detector uses the low-band energy, maximum to minimum 
ratio of the AMDF function and zero crossing to make the voicing
decision". Very well, but my algorithm made errors too often. 
Could anybody point me in the right direction?

2. In order to transmit the window energy, I use a well-known formula
for gain computing:
	gain=sqrt(prediction_error)*sqrt(pitch_period/window_length)
for the voiced windows and
	gain=sqrt(prediction_error)*sqrt(3/window_length)
for unvoiced windows.
In the F-1015 standard 'Analog to Digital Conversion of Voice by 2400
Bit/Second Linear Predictive Coding', they compute a "root-mean-square
preemphasized speech amplitude" which is used in the receiver for
gain adjustment. Does anybody know more about that?

Please respond by E-mail. Thank you in advance.

Luigi E. Bojan
Research Institute for Automation
P.O. Box 12-75
Bucharest 78100
Romania
Email: temdsp@roearn.ici.ac.ro
==========

-- 
    Dr. Cristian E. Toma   

    Philips Research Laboratories
    VLSI Design Automation and Testing
