On 2/24/2015 12:00 PM, Jerry Stuckle wrote:
On 2/24/2015 11:32 AM, FranK Turner-Smith G3VKI wrote:
"AndyW" wrote in message
...
On 24/02/2015 12:47, gareth wrote:
What is the point of digital voice when there are already AM, SSB
and FM for those who want to appear indistinguishable from CBers?

Perhaps it is cynicism from the manufacturers who introduce such things
as they see their traditional highly-priced corner of the market
being wiped away by SDR technologies?

Bandwidth reduction for one.
If you can encode and compress speech sufficiently then you can use
less bandwidth in transmission.

That's the bit I have trouble getting my head around. Back in the 1970s
and 1980s digital transmissions used a much greater bandwidth than their
analogue equivalents. Sampling at 2.2 x max frequency x number of bits
plus housekeeping bits etc. etc.
A UK standard 625 line PAL video transmission would have used a
bandwidth of over 400MHz!
Times have changed and left me behind, but I've still got me beer so who
cares?

But you forget compression. For instance, unless there is a scene
change, the vast majority of a television picture does not change from
frame to frame. Even if the camera moves, the picture shifts but
doesn't change all that much. Why waste all of that bandwidth resending
information the receiver already has?

And voice isn't continuous; it has lots of pauses. Some are very
noticeable, while others are so short we don't consciously hear them,
but they are there.

And once you've compressed everything you can out of the original
signal, you can do bit compression, similar to zipping a file for sending.

There are lots of ways to compress a signal before sending it digitally.
About the only one which can't be compressed is pure white noise -
which, of course, is only a concept (nothing is "pure").

I think that depends on what you mean by "pure". Sounds very
non-technical to me. Even noise can be compressed since if it is truly
noise, you don't need to send the data, just send the one bit that says
there is no signal, just noise. lol

A friend worked in sonar where the data was collected on ships and
transmitted via satellite to shore for signal processing rather than
doing any compression on the data and sending the useful info. As the
signal was nearly all "noise" trying to do any compression on it, even
the aspects that weren't "pure" white noise, would potentially have
masked the signals. Sonar is all about pulling the signal out of the
noise.

--

Rick

On 2/24/2015 5:47 PM, rickman wrote:
On 2/24/2015 12:00 PM, Jerry Stuckle wrote:
On 2/24/2015 11:32 AM, FranK Turner-Smith G3VKI wrote:
"AndyW" wrote in message
...
On 24/02/2015 12:47, gareth wrote:
What is the point of digital voice when there are already AM, SSB
and FM for those who want to appear indistinguishable from CBers?

Perhaps it is cynicism from the manufacturers who introduce such
things
as they see their traditional highly-priced corner of the market
being wiped away by SDR technologies?

Bandwidth reduction for one.
If you can encode and compress speech sufficiently then you can use
less bandwidth in transmission.

That's the bit I have trouble getting my head around. Back in the 1970s
and 1980s digital transmissions used a much greater bandwidth than their
analogue equivalents. Sampling at 2.2 x max frequency x number of bits
plus housekeeping bits etc. etc.
A UK standard 625 line PAL video transmission would have used a
bandwidth of over 400MHz!
Times have changed and left me behind, but I've still got me beer so who
cares?

But you forget compression. For instance, unless there is a scene
change, the vast majority of a television picture does not change from
frame to frame. Even if the camera moves, the picture shifts but
doesn't change all that much. Why waste all of that bandwidth resending
information the receiver already has?

And voice isn't continuous; it has lots of pauses. Some are very
noticeable, while others are so short we don't consciously hear them,
but they are there.

And once you've compressed everything you can out of the original
signal, you can do bit compression, similar to zipping a file for
sending.

There are lots of ways to compress a signal before sending it digitally.
About the only one which can't be compressed is pure white noise -
which, of course, is only a concept (nothing is "pure").

I think that depends on what you mean by "pure". Sounds very
non-technical to me. Even noise can be compressed since if it is truly
noise, you don't need to send the data, just send the one bit that says
there is no signal, just noise. lol


Pure white noise is a random distribution of signal across the entire
spectrum, with an equal distribution of frequencies over time. Like a
pure resistor or capacitor, it doesn't exist. But the noise IS the
signal. To recreate the noise, you have to sample the signal and
transmit it. However, since it is completely random, by definition no
compression is possible.

A friend worked in sonar where the data was collected on ships and
transmitted via satellite to shore for signal processing rather than
doing any compression on the data and sending the useful info. As the
signal was nearly all "noise" trying to do any compression on it, even
the aspects that weren't "pure" white noise, would potentially have
masked the signals. Sonar is all about pulling the signal out of the
noise.


You mean the signal can't be compressed? No way. Any non-random signal
can be compressed to some extent. How much depends on the signal and
the amount of processing power required to compress it. However, in
your example, the processing power to compress the signal would probably
have been greater than that required to process the original signal. So
if there wasn't enough power to process the signal on the ship, there
wouldn't be enough power to compress the near-white noise signal, either.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

On 24/02/2015 17:00, Jerry Stuckle wrote:

But you forget compression. For instance, unless there is a scene
change, the vast majority of a television picture does not change from
frame to frame. Even if the camera moves, the picture shifts but
doesn't change all that much. Why waste all of that bandwidth resending
information the receiver already has?

Which is why, on cheaper televisions, the picture tesselates when
showing random images such as rain, fire, waterfalls etc.
The true test of a quality television is to watch a waterfall or flames
and see it pin-sharp.
Cheaper TVs use cheap lower-powered decoding systems and for complex
images they do not have enough time to fully decode the image before the
next frame arrives.

Andy

On 2/25/2015 2:30 AM, AndyW wrote:
On 24/02/2015 17:00, Jerry Stuckle wrote:

But you forget compression. For instance, unless there is a scene
change, the vast majority of a television picture does not change from
frame to frame. Even if the camera moves, the picture shifts but
doesn't change all that much. Why waste all of that bandwidth resending
information the receiver already has?

Which is why, on cheaper televisions, the picture tesselates when
showing random images such as rain, fire, waterfalls etc.
The true test of a quality television is to watch a waterfall or flames
and see it pin-sharp.
Cheaper TVs use cheap lower-powered decoding systems and for complex
images they do not have enough time to fully decode the image before the
next frame arrives.

Andy


Not really true, at least in the United States. All TV's here use the
same (proprietary) chipsets to decompress the digital signal. However,
it makes a huge difference on the resolution being used, i.e. 720P,
1080P, 1080I, UHD... The difference is in what happens after the signal
is decompressed.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

En el artículo , FranK Turner-Smith
G3VKI escribió:

That's the bit I have trouble getting my head around. Back in the 1970s and
1980s digital transmissions used a much greater bandwidth than their
analogue equivalents. Sampling at 2.2 x max frequency x number of bits plus
housekeeping bits etc. etc.

One word: compression.

If we all took the same attitude as the OP we'd still be using Strowger
exchanges for the phone system. Thankfully, some people understand the
need for progress and aren't stuck in the past.

Times have changed and left me behind, but I've still got me beer so who
cares?

Good man

--
:: je suis Charlie :: yo soy Charlie :: ik ben Charlie ::

"Mike Tomlinson" wrote in message
...

If we all took the same attitude as the OP we'd still be using Strowger
exchanges for the phone system. Thankfully, some people understand the
need for progress and aren't stuck in the past.

There you go again with your one-sided infantile outbursts.

On 2/24/2015 1:28 PM, gareth wrote:
"Mike Tomlinson" wrote in message
...

If we all took the same attitude as the OP we'd still be using Strowger
exchanges for the phone system. Thankfully, some people understand the
need for progress and aren't stuck in the past.

There you go again with your one-sided infantile outbursts.

lol!

--

Rick

On 24/02/2015 16:32, FranK Turner-Smith G3VKI wrote:
"AndyW" wrote in message

Bandwidth reduction for one.
If you can encode and compress speech sufficiently then you can use
less bandwidth in transmission.

That's the bit I have trouble getting my head around. Back in the 1970s
and 1980s digital transmissions used a much greater bandwidth than their
analogue equivalents. Sampling at 2.2 x max frequency x number of bits
plus housekeeping bits etc. etc.

But then you add compression on top. As technology increases and the
ability to process data quickly advances you can real-time encode and
decode data at a frightening rate. Back when I started playing about
with digital sound we had enough speed to run-length encode in real
time, now with dedicated number cruncher chips you can carry out very
complex lossless sound compression in real time and for lo-fi sound you
can use lossy compression and have a lot of the band left over for a
time-slice share.
One of my final dissertation for university was on digital compression
techniques (lossy and lossless) and I get a bit geeky about it all :-)
Surprised I still remember it all....


Andy

On 2/24/2015 12:10 PM, Brian Morrison wrote:
On Tue, 24 Feb 2015 16:32:21 -0000
FranK Turner-Smith G3VKI wrote:

Bandwidth reduction for one.
If you can encode and compress speech sufficiently then you can use
less bandwidth in transmission.

That's the bit I have trouble getting my head around. Back in the
1970s and 1980s digital transmissions used a much greater bandwidth
than their analogue equivalents. Sampling at 2.2 x max frequency x
number of bits plus housekeeping bits etc. etc.

Have a look at David Rowe's web site about Codec 2 and his work on it.

http://rowetel.com

Most of the codec development effort goes into voice modelling that
allows redundant information to be thrown away without making the
encoded speech sound too horrible when decoded. And on working out
which bits in the encoded frame need to be better protected and which
don't, this is especially important when considering what encodes
voiced and non-voiced speech and ensuring it doesn't get mixed up.

Other than uLaw/Alaw, voice for telephony is not compressed in the same
ways that a zip file is. As you say, they model the vocal tract and
send the parameters for the sounds that are to be produced along with
error information to make it more intelligible. For sounds that aren't
voice or voice like, they are reproduced poorly. This is why low bit
rate compression on cell phones doesn't convey music very well and
background noise messes up the intelligibility much more than with uLaw
or ALaw compression which are just ways of compressing the waveform
without knowing anything about the content.

--

Rick

On 2/24/2015 7:47 AM, gareth wrote:
What is the point of digital voice when there are already AM, SSB
and FM for those who want to appear indistinguishable from CBers?

Perhaps it is cynicism from the manufacturers who introduce such things
as they see their traditional highly-priced corner of the market
being wiped away by SDR technologies?




Because it's there!

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================