| Author |
Message |
Dirk Bruere at Neopax
Guest
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 Posted:
Tue Nov 08, 2005 7:52 pm Post subject:
Volume Control - digital |
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I'm trying for a wireless solution to get rid of some cables.
'Obviously' the best is to use direct ditital stream from say a CD player,
transport it wirelessly and either convert it to analogue at the amp in the
speaker, or continue digitally into a digital amp eg Powersoft.
Problem is, how do I control the volume?
There are only two possible way that I can see:
a) Convert it to analogue at the CD end and redigitise.
b) Do the volume control digitally.
I can see the drawbacks of a), but what about b)?
Any s/w available to do it simply in a PC for example?
--
Dirk
The Consensus:-
The political party for the new millenium
http://www.theconsensus.org
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Richard Crowley
Guest
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| Posted:
Tue Nov 08, 2005 8:25 pm Post subject:
Re: Volume Control - digital |
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"Dirk Bruere at Neopax" wrote ...
| Quote: | I'm trying for a wireless solution to get rid of some cables.
'Obviously' the best is to use direct ditital stream from say
a CD player, transport it wirelessly and either convert it to
analogue at the amp in the speaker, or continue digitally
into a digital amp eg Powersoft.
Problem is, how do I control the volume?
There are only two possible way that I can see:
a) Convert it to analogue at the CD end and redigitise.
b) Do the volume control digitally.
I can see the drawbacks of a), but what about b)?
Any s/w available to do it simply in a PC for example?
|
You can use a PC for a volume control, but can't run a
wire?
A very quick scan of the Powersoft website revealed that
the amplifier models I looked at have integrated volume
controls. |
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Dirk Bruere at Neopax
Guest
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| Posted:
Tue Nov 08, 2005 8:43 pm Post subject:
Re: Volume Control - digital |
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Richard Crowley wrote:
| Quote: | "Dirk Bruere at Neopax" wrote ...
I'm trying for a wireless solution to get rid of some cables.
'Obviously' the best is to use direct ditital stream from say a CD
player, transport it wirelessly and either convert it to
analogue at the amp in the speaker, or continue digitally into a
digital amp eg Powersoft.
Problem is, how do I control the volume?
There are only two possible way that I can see:
a) Convert it to analogue at the CD end and redigitise.
b) Do the volume control digitally.
I can see the drawbacks of a), but what about b)?
Any s/w available to do it simply in a PC for example?
You can use a PC for a volume control, but can't run a
wire?
|
The system is in the >$20,000 range and the customers doesn't want wires
trailing about. They don't want to see anything except a few elegant (moveable)
speakers unobtrusively plugged into the mains.
| Quote: | A very quick scan of the Powersoft website revealed that
the amplifier models I looked at have integrated volume
controls.
|
That won't solve the problem because there is going to be one amp in each
speaker. The control must be done at the sending end. Unless there are
completely separate wireless volume controls as well...
--
Dirk
The Consensus:-
The political party for the new millenium
http://www.theconsensus.org |
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Richard Crowley
Guest
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| Posted:
Tue Nov 08, 2005 8:51 pm Post subject:
Re: Volume Control - digital |
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"Dirk Bruere at Neopax" <dirk.bruere@gmail.com> wrote in message
news:3tbrsqFrsa75U1@individual.net...
| Quote: | Richard Crowley wrote:
"Dirk Bruere at Neopax" wrote ...
I'm trying for a wireless solution to get rid of some cables.
'Obviously' the best is to use direct ditital stream from say a CD
player, transport it wirelessly and either convert it to
analogue at the amp in the speaker, or continue digitally into a
digital amp eg Powersoft.
Problem is, how do I control the volume?
There are only two possible way that I can see:
a) Convert it to analogue at the CD end and redigitise.
b) Do the volume control digitally.
I can see the drawbacks of a), but what about b)?
Any s/w available to do it simply in a PC for example?
You can use a PC for a volume control, but can't run a
wire?
The system is in the >$20,000 range and the customers doesn't want
wires trailing about. They don't want to see anything except a few
elegant (moveable) speakers unobtrusively plugged into the mains.
|
So design a custom composite "cable" and connector that
carry both the power and the signal. $20K is not enough
to develop a really reliable, high-fidelity wireless digital
solution.
| Quote: | A very quick scan of the Powersoft website revealed that
the amplifier models I looked at have integrated volume
controls.
That won't solve the problem because there is going to be one amp in
each speaker. The control must be done at the sending end. Unless
there are completely separate wireless volume controls as well...
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If you can work out a reliable way of sending the digital
audio signal via wireless, working out the volume control
is a trivial add-on. |
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Scott Dorsey
Guest
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| Posted:
Tue Nov 08, 2005 9:04 pm Post subject:
Re: Volume Control - digital |
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Dirk Bruere at Neopax <dirk.bruere@gmail.com> wrote:
| Quote: |
The system is in the >$20,000 range and the customers doesn't want wires
trailing about. They don't want to see anything except a few elegant (moveable)
speakers unobtrusively plugged into the mains.
|
In that case, you can probably afford one of the boxes from
Graham-Patten Systems. I believe they make a thing that does
just what you want.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis." |
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Dirk Bruere at Neopax
Guest
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| Posted:
Tue Nov 08, 2005 9:31 pm Post subject:
Re: Volume Control - digital |
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Richard Crowley wrote:
| Quote: |
"Dirk Bruere at Neopax" <dirk.bruere@gmail.com> wrote in message
news:3tbrsqFrsa75U1@individual.net...
Richard Crowley wrote:
"Dirk Bruere at Neopax" wrote ...
I'm trying for a wireless solution to get rid of some cables.
'Obviously' the best is to use direct ditital stream from say a CD
player, transport it wirelessly and either convert it to
analogue at the amp in the speaker, or continue digitally into a
digital amp eg Powersoft.
Problem is, how do I control the volume?
There are only two possible way that I can see:
a) Convert it to analogue at the CD end and redigitise.
b) Do the volume control digitally.
I can see the drawbacks of a), but what about b)?
Any s/w available to do it simply in a PC for example?
You can use a PC for a volume control, but can't run a
wire?
The system is in the >$20,000 range and the customers doesn't want
wires trailing about. They don't want to see anything except a few
elegant (moveable) speakers unobtrusively plugged into the mains.
So design a custom composite "cable" and connector that
carry both the power and the signal. $20K is not enough
to develop a really reliable, high-fidelity wireless digital
solution.
|
It does if we're selling dozens per year.
| Quote: | A very quick scan of the Powersoft website revealed that
the amplifier models I looked at have integrated volume
controls.
That won't solve the problem because there is going to be one amp in
each speaker. The control must be done at the sending end. Unless
there are completely separate wireless volume controls as well...
If you can work out a reliable way of sending the digital
audio signal via wireless, working out the volume control
is a trivial add-on.
|
Such a solution exists, at least in chip form from Nordic.
Being an EE I could develop a wireless solution from their reference designs,
but I'd rather not.
Hence my other Q on these NGs.
--
Dirk
The Consensus:-
The political party for the new millenium
http://www.theconsensus.org |
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Dirk Bruere at Neopax
Guest
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| Posted:
Tue Nov 08, 2005 9:32 pm Post subject:
Re: Volume Control - digital |
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Scott Dorsey wrote:
| Quote: | Dirk Bruere at Neopax <dirk.bruere@gmail.com> wrote:
The system is in the >$20,000 range and the customers doesn't want wires
trailing about. They don't want to see anything except a few elegant (moveable)
speakers unobtrusively plugged into the mains.
In that case, you can probably afford one of the boxes from
Graham-Patten Systems. I believe they make a thing that does
just what you want.
--scott
The wireless part is not the problem at present. |
I want advice on volume control.
--
Dirk
The Consensus:-
The political party for the new millenium
http://www.theconsensus.org |
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Scott Dorsey
Guest
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| Posted:
Tue Nov 08, 2005 9:45 pm Post subject:
Re: Volume Control - digital |
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In article <3tbuokFrlm6fU2@individual.net>,
Dirk Bruere at Neopax <dirk.bruere@gmail.com> wrote:
| Quote: | Scott Dorsey wrote:
Dirk Bruere at Neopax <dirk.bruere@gmail.com> wrote:
The system is in the >$20,000 range and the customers doesn't want wires
trailing about. They don't want to see anything except a few elegant (moveable)
speakers unobtrusively plugged into the mains.
In that case, you can probably afford one of the boxes from
Graham-Patten Systems. I believe they make a thing that does
just what you want.
The wireless part is not the problem at present.
I want advice on volume control.
|
Right. Graham-Patten makes a box with an AES/EBU in, an AES/EBU out, and
a knob. It lets you scale input down by any factor.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis." |
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Dirk Bruere at Neopax
Guest
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| Posted:
Tue Nov 08, 2005 9:57 pm Post subject:
Re: Volume Control - digital |
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Scott Dorsey wrote:
| Quote: | In article <3tbuokFrlm6fU2@individual.net>,
Dirk Bruere at Neopax <dirk.bruere@gmail.com> wrote:
Scott Dorsey wrote:
Dirk Bruere at Neopax <dirk.bruere@gmail.com> wrote:
The system is in the >$20,000 range and the customers doesn't want wires
trailing about. They don't want to see anything except a few elegant (moveable)
speakers unobtrusively plugged into the mains.
In that case, you can probably afford one of the boxes from
Graham-Patten Systems. I believe they make a thing that does
just what you want.
The wireless part is not the problem at present.
I want advice on volume control.
Right. Graham-Patten makes a box with an AES/EBU in, an AES/EBU out, and
a knob. It lets you scale input down by any factor.
--scott
|
Well, since it is going to be a PC storing and originating the digital signals I
was hoping for something in s/w.
Or at least an explanation of why this is not possible.
Given the type of system we are developing the fewer boxes the better.
--
Dirk
The Consensus:-
The political party for the new millenium
http://www.theconsensus.org |
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Scott Dorsey
Guest
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| Posted:
Tue Nov 08, 2005 10:12 pm Post subject:
Re: Volume Control - digital |
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Dirk Bruere at Neopax <dirk.bruere@gmail.com> wrote:
| Quote: |
Right. Graham-Patten makes a box with an AES/EBU in, an AES/EBU out, and
a knob. It lets you scale input down by any factor.
Well, since it is going to be a PC storing and originating the digital signals I
was hoping for something in s/w.
|
So, write some software. All you need is to take your existing software
and modify it to multiply everything by a constant. Then you pop up
something on the screen that lets the user change that constant.
What jukebox software are you using? What interface? What operating
system?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis." |
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Dirk Bruere at Neopax
Guest
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| Posted:
Tue Nov 08, 2005 10:28 pm Post subject:
Re: Volume Control - digital |
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Scott Dorsey wrote:
| Quote: | Dirk Bruere at Neopax <dirk.bruere@gmail.com> wrote:
Right. Graham-Patten makes a box with an AES/EBU in, an AES/EBU out, and
a knob. It lets you scale input down by any factor.
Well, since it is going to be a PC storing and originating the digital signals I
was hoping for something in s/w.
So, write some software. All you need is to take your existing software
and modify it to multiply everything by a constant. Then you pop up
something on the screen that lets the user change that constant.
|
That's what I thought, but I was wondering about digitisation noise if
everything gets (say) divided by 256. The 16 bit signal becomes 8 bit at low volume.
| Quote: | What jukebox software are you using? What interface? What operating
system?
--scott
|
Well, it's going to probably be MS Media Centre.
--
Dirk
The Consensus:-
The political party for the new millenium
http://www.theconsensus.org |
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Guest
|
| Posted:
Tue Nov 08, 2005 10:28 pm Post subject:
Re: Volume Control - digital |
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Scott Dorsey wrote:
| Quote: | Dirk Bruere at Neopax <dirk.bruere@gmail.com> wrote:
Right. Graham-Patten makes a box with an AES/EBU in, an AES/EBU out, and
a knob. It lets you scale input down by any factor.
Well, since it is going to be a PC storing and originating the digital signals I
was hoping for something in s/w.
So, write some software. All you need is to take your existing software
and modify it to multiply everything by a constant. Then you pop up
something on the screen that lets the user change that constant.
|
Well, it is, as I am sure Scott knows, a wee bit more complicated than
that.
You have a control object on the screen, say a slider control. It
outputs
an integer between some minimum and maximum value whenever it's
moved. Say it outputs a range from 0-127.
Take that value, and use it to look up a 15-bit gain coefficient in a
128
entry lookup table. This table is populated such that the linear range
of
0-127 is translated into an appropriate gain curve that "feels right",
i.e.
approximately logarithmic with lots of resolution where you need it
(upper
third), and lots of gain change where you need it (lower third).
Take the 15 bit gain coefficient (actually, it's really a 16 bit signed
integer coefficient limited to only the positive values: I'll explain
why in
a bit) and for each sample that comes flying by, multiply the two
together.
The result will be a 32-bit signed integer. TO get back to 16 bits, add
an
appropriate dither value (usually 16 bits) to the 32 bit result, then
take
the top 16 bits as the gain-adjusted sample. Repeat for all subsequent
samples.
If you want to get more sophisicated, hold on to the 16 lower bits and
feed
them back into the input stream after the multiply. Do it right, and
you can
add higher-order noise shaping to reduce the audible effect of the
dithering.
Always make sure your gain coefficients are positive, i.e., in the
range of
0x0000 to 0x7FFF (0 to 32767). If you don't, as soon as the top bit
gets
set, it' makes it a negative gain coefficient and you suddenly flip the
phase
of the resulting signal. Bad idea, especially when you run your volume
control up thourgh the transition from positive to negative gains. Bad
idea.
Oh, and you're likely to encounter some "fluttering" when you're
changing
volume often referred to as "zipper noise." Contrary to common belief,
it's
not because you only have a limited number of steps in your volume
control but because you aren't changing the gain OFTEN enough. The
RIGHT way to do it is to differentiate the steps coming from your
volume
control, thus getting effectively the SPEED of the knob, not its
position.
With that, you can make a prediction of how fast you have to change
your
gain. You're gain rampling algorithm then continuously ramps the gain
at fairly quick intervale (1000x a second, maybe), between the previous
value and the next value of the vaolume control. Do it right, and no
zipper noise, ever, no matter how many of few steps you have in your
volume control.
Basically, it's not a half-hour programming excercise. |
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Scott Dorsey
Guest
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| Posted:
Tue Nov 08, 2005 10:29 pm Post subject:
Re: Volume Control - digital |
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Dirk Bruere at Neopax <dirk.bruere@gmail.com> wrote:
| Quote: | Scott Dorsey wrote:
Dirk Bruere at Neopax <dirk.bruere@gmail.com> wrote:
Right. Graham-Patten makes a box with an AES/EBU in, an AES/EBU out, and
a knob. It lets you scale input down by any factor.
Well, since it is going to be a PC storing and originating the digital signals I
was hoping for something in s/w.
So, write some software. All you need is to take your existing software
and modify it to multiply everything by a constant. Then you pop up
something on the screen that lets the user change that constant.
That's what I thought, but I was wondering about digitisation noise if
everything gets (say) divided by 256. The 16 bit signal becomes 8 bit at low volume.
|
Right, that's how it works. The lower the level, the poorer the S/N
you get. Just like with analogue gear.
| Quote: | What jukebox software are you using? What interface? What operating
system?
Well, it's going to probably be MS Media Centre.
|
I'm terribly sorry.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis." |
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Guest
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| Posted:
Tue Nov 08, 2005 10:32 pm Post subject:
Re: Volume Control - digital |
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Dirk Bruere at Neopax wrote:
| Quote: | Scott Dorsey wrote:
So, write some software. All you need is to take your existing software
and modify it to multiply everything by a constant. Then you pop up
something on the screen that lets the user change that constant.
That's what I thought, but I was wondering about digitisation noise if
everything gets (say) divided by 256. The 16 bit signal becomes 8 bit at low
volume.
|
See my detailed reply elswhere. Bascially, you multiply your 16-bit
sample
value by a 16 bit gain coefficient, which results in a 32 bit result.
Before
truncating, you dither or noise shape to eliminate quantization
artifacts.
What kind of dither or how you noise shape is what separates the DSP
men from the boys. |
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Guest
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| Posted:
Tue Nov 08, 2005 10:35 pm Post subject:
Re: Volume Control - digital |
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Dirk Bruere at Neopax wrote:
| Quote: | The 16 bit signal becomes 8 bit at low volume.
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Yes, it does. That's what makes it "low volume."
Read the text elsewgere on how to deal with the artifacts resulting. |
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