[Q]Audio processing technique to increase speech quality?

<heliboy2003@yahoo.com.tw> wrote in message
news:1192586067.094892.27230@z24g2000prh.googlegroups.com...
> Hi,
>
> I am in a process to improve the speech quality out of our current
> speech codec. Basically, our speech codec is an ADPCM codec

[...]

It is well known that ADPCM sucks, especially for the low bit rate. Why
reinventing the wheels and not using any of the standard speech coders?

Vladimir Vassilevsky
DSP and Mixed Signal Consultant
www.abvolt.com

heliboy2003@yahoo.com.tw writes:

>> I assumed the definition of "improve the speech quality" meant "improve
>> the listening experience of a person".
>
>
> Exactly!! I am thinking that adding some audio effects (such like
> flanger) to the decoded speech could masked out some of the embedded
> noise resulting from the encoding/decoding (ADPCM) process, so that
> people can feel the decoded speech better than without adding such
> effects. I just don't know if adding such audio effect is a common
> practice or just I am too stupid and bold to think that.

I think that's a horrible idea and a horrible philosophy. Why not
apply the extra processing to improving the fundamental codec? For
example, with a higher sampling rate you could reduce the noise.

Also, I think Vladimir's question is excellent: "Why reinvent the
wheels?" 
-- 
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%% Fuquay-Varina, NC            %            on, and she's also a telephone."
%%% 919-577-9882                % 
%%%% <yates@ieee.org>           %        'Yours Truly, 2095', *Time*, ELO   
http://www.digitalsignallabs.com

> Also, I think Vladimir's question is excellent: "Why reinvent the
> wheels?"
> --

Hi, the ADPCM codec is standardized, we have no freedom to either
modify it or use other better codecs.
Unless I can convince my boss to send a proposal to persuade standard
body to change to a better codec.

>
> Also, I think Vladimir's question is excellent: "Why reinvent the
> wheels?"
> --

Hi, because that ADPCM codec is standardized. We can only try to play
some tricks to cheat the user's ear, not to convince the standard body
to chnage their codec.

heliboy2003@yahoo.com.tw writes:

>> Also, I think Vladimir's question is excellent: "Why reinvent the
>> wheels?"
>> --
>
> Hi, the ADPCM codec is standardized, we have no freedom to either
> modify it or use other better codecs.
> Unless I can convince my boss to send a proposal to persuade standard
> body to change to a better codec.

What is your application? 
-- 
%  Randy Yates                  % "Though you ride on the wheels of tomorrow,
%% Fuquay-Varina, NC            %  you still wander the fields of your
%%% 919-577-9882                %  sorrow."
%%%% <yates@ieee.org>           % '21st Century Man', *Time*, ELO
http://www.digitalsignallabs.com

heliboy2003@yahoo.com.tw wrote:
>> Also, I think Vladimir's question is excellent: "Why reinvent the
>> wheels?"
>> --
> 
> Hi, because that ADPCM codec is standardized. We can only try to play
> some tricks to cheat the user's ear, not to convince the standard body
> to chnage their codec.

It seems that you believe there is only one ADPCM standard. There are 
many. If you control both ends, you can choose an appropriate one.

The ITU defines several speech codecs which use ADPCM:

Codec    Sampling
G.         Rate
Number     (kHz)   Bit Rates (kBps)
G.721        8    32
G.726        8    16, 24, 32, 40, 64
G.727        8    16, 24, 32, 40, 64

Jerry
-- 
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Jerry Avins wrote:


>> Hi, because that ADPCM codec is standardized. We can only try to play
>> some tricks to cheat the user's ear, not to convince the standard body
>> to chnage their codec.
> 
> 
> It seems that you believe there is only one ADPCM standard. There are 
> many. If you control both ends, you can choose an appropriate one.
> 
> The ITU defines several speech codecs which use ADPCM:
> 
> Codec    Sampling
> G.         Rate
> Number     (kHz)   Bit Rates (kBps)
> G.721        8    32
> G.726        8    16, 24, 32, 40, 64
> G.727        8    16, 24, 32, 40, 64

There is also G.722 at 16kHz/64kbps as well as IMA and MS ADPCM scalable 
to whatever sample rate (4 bits per sample). But any kind of ADPCM 
requires at least 32kbps to produce the toll quality speech. Below 
32kbps, the ADPCM sound is nasty. It seems like the OP got stuck with 
some particular codec realization.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com