[pb]

I corrected the DC offset so the base line is centered, but I can't really
hear the difference. Because the original baseline moved toward the
bottom, the bottom part was much shorter than the part above the baseline.
With that, you can't normalize it further. The volume is low since the
upper side is over the edge. How can the audio like this be further
enhanced?

I also found some recorded audio without DC offset problem but has a
little bit difference in length below and above the baseline. Is it
normal? What does it tell about the recording device?

Thanks for the help,

[Serge Auckland[_2_]]

"pb" wrote in message
...
I corrected the DC offset so the base line is centered, but I can't really
hear the difference. Because the original baseline moved toward the
bottom, the bottom part was much shorter than the part above the baseline.
With that, you can't normalize it further. The volume is low since the
upper side is over the edge. How can the audio like this be further
enhanced?

I also found some recorded audio without DC offset problem but has a
little bit difference in length below and above the baseline. Is it
normal? What does it tell about the recording device?

Thanks for the help,

The instantaneous amplitude of any piece of audio will not be symmetrical
about the base line in the short-term. Voice especially is asymmetrical, but
so are many instruments. In the long-term, it all averages out provided of
course there are no DC offset problems with the recording device. The issue
is well recognised in Broadcast, especially AM, where it is possible to
exceed 100% modulation in the positive direction, but not in the negative
direction. Consequently, AM processors include phase rotators which ensure
that the highest modulation is always positive. 125%, even 150% positive mod
is possible where permitted by regulation (The UK does NOT allow more than
100% mod)

With naturally occurring audio, the overall *energy* of audio is balanced
between positive and negative excursions, as air doesn't support a "DC"
offset, but in the short-term, (I'm talking mS) there's considerable
difference. Have a look at the waveform of an Oboe for example, or as
mentioned above, speech.

S.


--
http://audiopages.googlepages.com

[Richard Crowley]

"pb" wrote ...
I corrected the DC offset so the base line is centered, but I
can't really hear the difference.

DC offset is not generally an audible factor for music, speech,
etc. But it is important in other areas. For example, if you
make a CD with a track with DC offset, there will be a step-
function ("click") at the beginning and the end where the player
mutes, etc. etc.

Because the original baseline moved toward the bottom,
the bottom part was much shorter than the part above the
baseline.

Asymetrical waveforms are quite common in both music
and speech.

With that, you can't normalize it further.

Normalization of level is a separate function from DC
offset manipulation.

Normalization is referenced to the peak level(s), whether
they are positive or negative. You wouldn't want to change
the amplitude of the negative or positive parts of the
waveform independently.

The volume is low since the upper side is over the edge.

I'm not sure what that means?

How can the audio like this be further enhanced?

What do you mean by "enhanced"?

I also found some recorded audio without DC offset problem
but has a little bit difference in length below and above the
baseline. Is it normal?

Yes, it is quite normal.

What does it tell about the recording device?

It may tell nothing at all about the recording device.

You didn't mention....
What you are recording.
What you are recording it with.
What you are using to view/edit/listen.
What are the problem(s?) with the recording that you are
trying to fix.

An actual sample is worth 10,000 words. Post a brief (10-20 sec)
representative clip of the WAV file online somewhere and post
the URL here. (NOTE: This is a text-only newsgroup and not
appropriate to post binary attachments here.)

[Don Pearce]

Serge Auckland wrote:

"pb" wrote in message
...
I corrected the DC offset so the base line is centered, but I can't
really
hear the difference. Because the original baseline moved toward the
bottom, the bottom part was much shorter than the part above the
baseline.
With that, you can't normalize it further. The volume is low since the
upper side is over the edge. How can the audio like this be further
enhanced?

I also found some recorded audio without DC offset problem but has a
little bit difference in length below and above the baseline. Is it
normal? What does it tell about the recording device?

Thanks for the help,

The instantaneous amplitude of any piece of audio will not be
symmetrical about the base line in the short-term. Voice especially is
asymmetrical, but so are many instruments. In the long-term, it all
averages out provided of course there are no DC offset problems with the
recording device. The issue is well recognised in Broadcast, especially
AM, where it is possible to exceed 100% modulation in the positive
direction, but not in the negative direction. Consequently, AM
processors include phase rotators which ensure that the highest
modulation is always positive. 125%, even 150% positive mod is possible
where permitted by regulation (The UK does NOT allow more than 100% mod)

There's nothing to stop you exceeding 100% mod in the negative direction
if you do it right, and recover with a synchronous demodulator. I've
done it myself and recovered undistorted modulation.

When I say do it right, I mean using a double balanced mixer followed by
a linear amp. Obviously you can't do it when modulating an output
valve's anode.

d

[Don Pearce]

pb wrote:
I corrected the DC offset so the base line is centered, but I can't really
hear the difference. Because the original baseline moved toward the
bottom, the bottom part was much shorter than the part above the baseline.
With that, you can't normalize it further. The volume is low since the
upper side is over the edge. How can the audio like this be further
enhanced?

I also found some recorded audio without DC offset problem but has a
little bit difference in length below and above the baseline. Is it
normal? What does it tell about the recording device?

Thanks for the help,


DC offset is what you get in a plane. You cure it by holding your nose
and blowing. You can hear it, or rather you are aware of the effect; it
makes you deaf.

d

[Serge Auckland[_2_]]

"Don Pearce" wrote in message
...
Serge Auckland wrote:

"pb" wrote in message
...
I corrected the DC offset so the base line is centered, but I can't
really
hear the difference. Because the original baseline moved toward the
bottom, the bottom part was much shorter than the part above the
baseline.
With that, you can't normalize it further. The volume is low since the
upper side is over the edge. How can the audio like this be further
enhanced?

I also found some recorded audio without DC offset problem but has a
little bit difference in length below and above the baseline. Is it
normal? What does it tell about the recording device?

Thanks for the help,

The instantaneous amplitude of any piece of audio will not be symmetrical
about the base line in the short-term. Voice especially is asymmetrical,
but so are many instruments. In the long-term, it all averages out
provided of course there are no DC offset problems with the recording
device. The issue is well recognised in Broadcast, especially AM, where
it is possible to exceed 100% modulation in the positive direction, but
not in the negative direction. Consequently, AM processors include phase
rotators which ensure that the highest modulation is always positive.
125%, even 150% positive mod is possible where permitted by regulation
(The UK does NOT allow more than 100% mod)

There's nothing to stop you exceeding 100% mod in the negative direction
if you do it right, and recover with a synchronous demodulator. I've done
it myself and recovered undistorted modulation.

When I say do it right, I mean using a double balanced mixer followed by a
linear amp. Obviously you can't do it when modulating an output valve's
anode.

d

I'm not sure I understand what you mean. When you get to 100% negative
modulation the carrier's amplitude is zero, so I don't see how you can get
to less than zero carrier amplitude. I'm talking about standard
double-sideband AM, not Single Sideband or suppressed carrier modulations.

S.
--
http://audiopages.googlepages.com

[Don Pearce]

Serge Auckland wrote:

"Don Pearce" wrote in message
...
Serge Auckland wrote:

"pb" wrote in message
...
I corrected the DC offset so the base line is centered, but I can't
really
hear the difference. Because the original baseline moved toward the
bottom, the bottom part was much shorter than the part above the
baseline.
With that, you can't normalize it further. The volume is low since the
upper side is over the edge. How can the audio like this be further
enhanced?

I also found some recorded audio without DC offset problem but has a
little bit difference in length below and above the baseline. Is it
normal? What does it tell about the recording device?

Thanks for the help,

The instantaneous amplitude of any piece of audio will not be
symmetrical about the base line in the short-term. Voice especially
is asymmetrical, but so are many instruments. In the long-term, it
all averages out provided of course there are no DC offset problems
with the recording device. The issue is well recognised in Broadcast,
especially AM, where it is possible to exceed 100% modulation in the
positive direction, but not in the negative direction. Consequently,
AM processors include phase rotators which ensure that the highest
modulation is always positive. 125%, even 150% positive mod is
possible where permitted by regulation (The UK does NOT allow more
than 100% mod)

There's nothing to stop you exceeding 100% mod in the negative
direction if you do it right, and recover with a synchronous
demodulator. I've done it myself and recovered undistorted modulation.

When I say do it right, I mean using a double balanced mixer followed
by a linear amp. Obviously you can't do it when modulating an output
valve's anode.

d

I'm not sure I understand what you mean. When you get to 100% negative
modulation the carrier's amplitude is zero, so I don't see how you can
get to less than zero carrier amplitude. I'm talking about standard
double-sideband AM, not Single Sideband or suppressed carrier modulations.

S.

Yes. What happens is the bottom of the sine wave carries on past zero
and up the other side, but with the carrier phase reversed. A
synchronous detector recovers it quite happily.

d

[Eeyore]

pb wrote:

I corrected the DC offset so the base line is centered, but I can't really
hear the difference.

Because there's no difference to hear.

Graham

[Don Pearce]

On Sun, 18 May 2008 15:57:12 +0100, "Serge Auckland"
wrote:


"Don Pearce" wrote in message
...
Serge Auckland wrote:

"pb" wrote in message
...
I corrected the DC offset so the base line is centered, but I can't
really
hear the difference. Because the original baseline moved toward the
bottom, the bottom part was much shorter than the part above the
baseline.
With that, you can't normalize it further. The volume is low since the
upper side is over the edge. How can the audio like this be further
enhanced?

I also found some recorded audio without DC offset problem but has a
little bit difference in length below and above the baseline. Is it
normal? What does it tell about the recording device?

Thanks for the help,

The instantaneous amplitude of any piece of audio will not be symmetrical
about the base line in the short-term. Voice especially is asymmetrical,
but so are many instruments. In the long-term, it all averages out
provided of course there are no DC offset problems with the recording
device. The issue is well recognised in Broadcast, especially AM, where
it is possible to exceed 100% modulation in the positive direction, but
not in the negative direction. Consequently, AM processors include phase
rotators which ensure that the highest modulation is always positive.
125%, even 150% positive mod is possible where permitted by regulation
(The UK does NOT allow more than 100% mod)

There's nothing to stop you exceeding 100% mod in the negative direction
if you do it right, and recover with a synchronous demodulator. I've done
it myself and recovered undistorted modulation.

When I say do it right, I mean using a double balanced mixer followed by a
linear amp. Obviously you can't do it when modulating an output valve's
anode.

d

I'm not sure I understand what you mean. When you get to 100% negative
modulation the carrier's amplitude is zero, so I don't see how you can get
to less than zero carrier amplitude. I'm talking about standard
double-sideband AM, not Single Sideband or suppressed carrier modulations.

S.

I've made an AVI animation with Mathcad of a carrier and AM. It starts
at zero mod, and winds its way up to 200% AM. You can see that it is
recoverable with a decent synchronous demod. The file is 1MB, so it
may be a little slow to get.

http://81.174.169.10/odds/am200.avi

d
--
Pearce Consulting
http://www.pearce.uk.com

[Serge Auckland[_2_]]

"Don Pearce" wrote in message
...
On Sun, 18 May 2008 15:57:12 +0100, "Serge Auckland"
wrote:


"Don Pearce" wrote in message
...
Serge Auckland wrote:

"pb" wrote in message
...
I corrected the DC offset so the base line is centered, but I can't
really
hear the difference. Because the original baseline moved toward the
bottom, the bottom part was much shorter than the part above the
baseline.
With that, you can't normalize it further. The volume is low since the
upper side is over the edge. How can the audio like this be further
enhanced?

I also found some recorded audio without DC offset problem but has a
little bit difference in length below and above the baseline. Is it
normal? What does it tell about the recording device?

Thanks for the help,

The instantaneous amplitude of any piece of audio will not be
symmetrical
about the base line in the short-term. Voice especially is
asymmetrical,
but so are many instruments. In the long-term, it all averages out
provided of course there are no DC offset problems with the recording
device. The issue is well recognised in Broadcast, especially AM, where
it is possible to exceed 100% modulation in the positive direction, but
not in the negative direction. Consequently, AM processors include
phase
rotators which ensure that the highest modulation is always positive.
125%, even 150% positive mod is possible where permitted by regulation
(The UK does NOT allow more than 100% mod)

There's nothing to stop you exceeding 100% mod in the negative direction
if you do it right, and recover with a synchronous demodulator. I've
done
it myself and recovered undistorted modulation.

When I say do it right, I mean using a double balanced mixer followed by
a
linear amp. Obviously you can't do it when modulating an output valve's
anode.

d

I'm not sure I understand what you mean. When you get to 100% negative
modulation the carrier's amplitude is zero, so I don't see how you can get
to less than zero carrier amplitude. I'm talking about standard
double-sideband AM, not Single Sideband or suppressed carrier modulations.

S.

I've made an AVI animation with Mathcad of a carrier and AM. It starts
at zero mod, and winds its way up to 200% AM. You can see that it is
recoverable with a decent synchronous demod. The file is 1MB, so it
may be a little slow to get.

http://81.174.169.10/odds/am200.avi

d
--
Pearce Consulting
http://www.pearce.uk.com

Thanks for that, most interesting. I assume that if it was demodulated with
a standard envelope detector the distortion would be horrendous.

As you are probably aware, my background is in Broadcast, and the idea of
greater than 100% negative mod just goes against the grain.

S.

--
http://audiopages.googlepages.com

[Richard Crowley]

"Serge Auckland" wrote ...
As you are probably aware, my background is in Broadcast, and the idea
of greater than 100% negative mod just goes against the grain.

Not to mention illegal depending on where you are. :-)

[Don Pearce]

On Sun, 18 May 2008 17:01:02 +0100, "Serge Auckland"
wrote:

Thanks for that, most interesting. I assume that if it was demodulated with
a standard envelope detector the distortion would be horrendous.

As you are probably aware, my background is in Broadcast, and the idea of
greater than 100% negative mod just goes against the grain.

S.

Welcome. I was in measurement and signal generation, so stopping at
100% just wasn't an option.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Chronic Philharmonic]

"Don Pearce" wrote in message
...
On Sun, 18 May 2008 17:01:02 +0100, "Serge Auckland"
wrote:

Thanks for that, most interesting. I assume that if it was demodulated
with
a standard envelope detector the distortion would be horrendous.

As you are probably aware, my background is in Broadcast, and the idea of
greater than 100% negative mod just goes against the grain.

S.

Welcome. I was in measurement and signal generation, so stopping at
100% just wasn't an option.

Carrier cut-off defines 100% modulation for continuous carrier double
sideband AM as used in the AM broadcast services. With the kind of
modulators used in this service, negative overmodulation is analogous to
(and indistinguishable from) clipping the baseband on negative peaks (the
carrier does *not* become inverted in phase). AM broadcast transmitters can
be overmodulated in the positive direction if they have adequate headroom to
pull it off. In the US, the FCC allows asymmetric modulation: 100% on
negative peaks, and 110% on positive peaks (the last time I checked).

The FCC does not allow negative overmodulation because of the sideband
splatter caused by the carrier cutoff, and because most AM receivers use
envelope demodulators, which cannot accommodate negative overmodulation,
even if the transmitters could do the carrier phase reversal.