adding dither in audio signals

hi,
   I had certain querries about adding dither in audio signals.
1) I presume one of the reasons to add it is to compensate for
quantisation error while
    converting analog to digital. Is there any other reason for adding
it?
2) Is it added only when the signal strength is zero, or would it be
advantageous to add it
    always. If quantization error is the primary consideration, I
presume it would be
    advantageous to add it always. But it seems that there are some
systems,
    where its added  only when the signal strength is zero for
sufficient period of time.

thanks
ganesh

gans1973@rediffmail.com wrote:

>    I had certain querries about adding dither in audio signals.
> 1) I presume one of the reasons to add it is to compensate for
> quantisation error while converting analog to digital. 
> Is there any other reason for adding it?

Adding dither is the only way to acquire signals with amplitudes
below 1/2 LSB.

> 2) Is it added only when the signal strength is zero, or would it be
> advantageous to add it
>     always.

You must add dither always during quantization, and when
changing the amplitude of a quantized signal. If the signal is
really zero (binary 0) adding dither makes no sense to me.

bye
Andreas
--
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gans1973@rediffmail.com writes:

> hi,
>    I had certain querries about adding dither in audio signals.
> 1) I presume one of the reasons to add it is to compensate for
> quantisation error while
>     converting analog to digital. Is there any other reason for adding
> it?

No.

> 2) Is it added only when the signal strength is zero, or would it be
> advantageous to add it
>     always. If quantization error is the primary consideration, I
> presume it would be
>     advantageous to add it always. But it seems that there are some
> systems,
>     where its added  only when the signal strength is zero for
> sufficient period of time.

Keep it on all the time. To go back and forth between dither/no dither
is to modulate your noise floor, and that's not a good thing.
-- 
%  Randy Yates                  % "Midnight, on the water... 
%% Fuquay-Varina, NC            %  I saw...  the ocean's daughter." 
%%% 919-577-9882                % 'Can't Get It Out Of My Head' 
%%%% <yates@ieee.org>           % *El Dorado*, Electric Light Orchestra
http://home.earthlink.net/~yatescr

>hi,
>   I had certain querries about adding dither in audio signals.
>1) I presume one of the reasons to add it is to compensate for
>quantisation error while
>    converting analog to digital. Is there any other reason for adding
>it?
>2) Is it added only when the signal strength is zero, or would it be
>advantageous to add it
>    always. If quantization error is the primary consideration, I
>presume it would be
>    advantageous to add it always. But it seems that there are some
>systems,
>    where its added  only when the signal strength is zero for
>sufficient period of time.
>
>thanks
>ganesh
>
>


Add dither all the time to the signal whenever you convert it from analog
to digital, irrespective of its signal strength. I don't see dither is
helpful for anything other than alleviating the quantization error.

- Krishna

Randy Yates wrote:
> gans1973@rediffmail.com writes:
> 
> 
>>hi,
>>   I had certain querries about adding dither in audio signals.
>>1) I presume one of the reasons to add it is to compensate for
>>quantisation error while
>>    converting analog to digital. Is there any other reason for adding
>>it?
> 
> 
> No.

Eh? Wouldn't you dither when changing the number of bits of a signal 
which is already digital? Wouldn't you dither within an IIR to mitigate 
the awfulness of those things?

>>2) Is it added only when the signal strength is zero, or would it be
>>advantageous to add it
>>    always. If quantization error is the primary consideration, I
>>presume it would be

Steve

Steve Underwood wrote:

>>>   I had certain querries about adding dither in audio signals.
>>> 1) I presume one of the reasons to add it is to compensate for
>>> quantisation error while
>>>    converting analog to digital. Is there any other reason for adding
>>> it?
>>
>> No.
> 
> Eh? Wouldn't you dither when changing the number of bits of a signal 
> which is already digital? 

Or when changing the sampling rate to a higher (presumably oversampled)
rate for the purpose of simplifying the D/A conversion filter. (right?)

Carlos
--

Steve Underwood <steveu@dis.org> writes:

> Randy Yates wrote:
>> gans1973@rediffmail.com writes:
>>
>>>hi,
>>>   I had certain querries about adding dither in audio signals.
>>>1) I presume one of the reasons to add it is to compensate for
>>>quantisation error while
>>>    converting analog to digital. Is there any other reason for adding
>>>it?
>> No.
>
> Eh? Wouldn't you dither when changing the number of bits of a signal
> which is already digital? Wouldn't you dither within an IIR to
> mitigate the awfulness of those things?

I took the OP's question to be "When you add it during A/D, is the only
reason to compensate for quantization error?" and not "Are there any
other situations in which you use dither?"
-- 
%  Randy Yates                  % "...the answer lies within your soul
%% Fuquay-Varina, NC            %       'cause no one knows which side
%%% 919-577-9882                %                   the coin will fall."
%%%% <yates@ieee.org>           %  'Big Wheels', *Out of the Blue*, ELO
http://home.earthlink.net/~yatescr

Randy Yates wrote:
> gans1973@rediffmail.com writes:
> 
> 
>>hi,
>>   I had certain querries about adding dither in audio signals.
>>1) I presume one of the reasons to add it is to compensate for
>>quantisation error while
>>    converting analog to digital. Is there any other reason for adding
>>it?
> 
> 
> No.

How about converting digital of one amplitude to another (gain change)?

>>2) Is it added only when the signal strength is zero, or would it be
>>advantageous to add it
>>    always. If quantization error is the primary consideration, I
>>presume it would be
>>    advantageous to add it always. But it seems that there are some
>>systems,
>>    where its added  only when the signal strength is zero for
>>sufficient period of time.
> 
> 
> Keep it on all the time. To go back and forth between dither/no dither
> is to modulate your noise floor, and that's not a good thing.

OT: It's snowing heavily in Central NJ right now. The grass is covered, 
but not thee pavement (yet).

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

Jerry Avins <jya@ieee.org> writes:

> Randy Yates wrote:
>> gans1973@rediffmail.com writes:
>>
>>>hi,
>>>   I had certain querries about adding dither in audio signals.
>>>1) I presume one of the reasons to add it is to compensate for
>>>quantisation error while
>>>    converting analog to digital. Is there any other reason for adding
>>>it?
>> No.
>
> How about converting digital of one amplitude to another (gain change)?

See my other post.

>>>2) Is it added only when the signal strength is zero, or would it be
>>>advantageous to add it
>>>    always. If quantization error is the primary consideration, I
>>>presume it would be
>>>    advantageous to add it always. But it seems that there are some
>>>systems,
>>>    where its added  only when the signal strength is zero for
>>>sufficient period of time.
>> Keep it on all the time. To go back and forth between dither/no
>> dither
>> is to modulate your noise floor, and that's not a good thing.
>
> OT: It's snowing heavily in Central NJ right now. The grass is
> covered, but not thee pavement (yet).

It's a lovely Spring day, in the 70s, here in central NC. 
-- 
%  Randy Yates                  % "My Shangri-la has gone away, fading like 
%% Fuquay-Varina, NC            %  the Beatles on 'Hey Jude'" 
%%% 919-577-9882                %  
%%%% <yates@ieee.org>           % 'Shangri-La', *A New World Record*, ELO
http://home.earthlink.net/~yatescr

Doesnt applying dither during sample rate conversion or for adding more
number of
bits in an already digitized signal directly or indirectly based on
reducing quantization error??

     Secondly, if the ADC is say 40 bits (or some v. high number of
bits) would
it still make sense to dither?? At 40 bits, the normal noise in a
system may
override the quantization error, and the system noise may itself act as
dither??


ganesh

Carlos Moreno wrote:
> Steve Underwood wrote:
>
> >>>   I had certain querries about adding dither in audio signals.
> >>> 1) I presume one of the reasons to add it is to compensate for
> >>> quantisation error while
> >>>    converting analog to digital. Is there any other reason for adding
> >>> it?
> >>
> >> No.
> >
> > Eh? Wouldn't you dither when changing the number of bits of a signal
> > which is already digital?
>
> Or when changing the sampling rate to a higher (presumably oversampled)
> rate for the purpose of simplifying the D/A conversion filter. (right?)
> 
> Carlos
> --