On Mon, 13 Mar 2006 18:37:33 +0000, Kevin Seal wrote:

In message , Rich Wilson
writes

"Serge Auckland" wrote in message
...

"Kevin Seal" wrote in message
...
In message , Serge Auckland
writes

"Kevin Seal" wrote in message
.. .
In message , Serge Auckland
writes

(snip)

The EBU (European Broadcasting Union) have defined 0dBFS digital to
mean
+18dBu analogue after conversion.


Interesting.
Can you let me have a reference to the technical paper for that.
Cheers,


EBU R68-2000. I'm emailing you a copy directly.

Received, thanks.

With 0dBFS as =18dBU, that would mean OVU (+4dBU) would be -14dBFS. Most
people I know line-up their Pro Tools rigs for -18dBFS for 0VU hence
OdBFS is going to be +22dBU.
Isn't it a lovely world!

Standard are great, that's why we have so many of them!

Decibels, to me, seem to be overused, particularly with digital audio. And
particularly because silence is negative infinity decibels, which isn't a
lot of good if you're writing a computer program that can only cope with
real numbers. What's wrong with plain old 0% to 100%?!
(Rhetorical question, don't feel obliged to answer...)

Are you trying to put us out of a job?

Not much danger of that, if he's such a bad programmer! :-)

BTW, what's wrong with 0-100% is that our hearing is logarithmic, so
deciBels give a much better idea of how things sound. A 10dB increase
in SPL sounds twice as loud, but takes ten times the power.

--

Stewart Pinkerton | Music is Art - Audio is Engineering

In article ,
Serge Auckland wrote:
Digital outputs are referred to maximum digital output (when all the
bits are 1) and that is called 0dBFS (0dB Full Scale). It has NO
analogue equivalent, as analogue can keep getting bigger without limit,
digital can't get any bigger than when all the bits are 1. In
Digital-Analogue conversion, a number of different conversion levels
have become more-or-less standard. The EBU (European Broadcasting
Union) have defined 0dBFS digital to mean +18dBu analogue after
conversion. The USA prefers that 0dBFS = +24dBu because that provides
20dB headroom above 0VU. A few dissidents prefer +25dBu as that's 1dB
better than +24...........

It's quite interesting to look at levels off Freeview. I lined up the
workshop receiver to read PPM 4 on a rare occasion when there was a test
card and line up tone available. And as expected TV progs peak to no more
than PPM 6. But some of the radio ones wrap the PPMs round the end stops.
;-)

My best Freeview receiver out of several is a Sony VTX-D800U and when I
changed it from the previous freebie Sagem which kept crashing I
immediately noticed the audio level was low. Switch the set from the same
channel on analogue to Freeview via a SCART and the difference was too
much. Correspondence with Sony showed that they thought the TV
broadcasters would peak to 0dBFS on FreeView instead of using the normal
EBU line up of peak being -10 dBFS.

--
*Re-elect nobody

Dave Plowman London SW
To e-mail, change noise into sound.

dbm is as stated a reference of two like power values to a 1mW reference
however the impedence does not need to be 600 ohms, it can be any value of
ohms as long as both power values are based on the same impedence

dbu is not unloaded but db(micro) it is as above but with a reference of
1microWatt it is not actually a u but the greek character mu

dbv would be a ratio based on two voltage levels and a reference of 1 volt

power db caclulations are 10 log Pout/Pin
Voltage db calculations are 20 log Vout/Vin

dbFS is "decibels full scale". It is an abbreviation for decibel amplitude
levels in digital systems which have a maximum available level (like PCM
encoding). 0 dBFS is assigned to the maximum possible level. There is still
the potential for ambiguity, since some use the RMS value of a full-scale
square wave for 0 dBFS, and some use a sine wave.

this is treated the same as voltag calculations because it is based on the
signal to noise ratio.

"David Peters (UK)" wrote in message
...
On 12 Mar 2006, Serge Auckland wrote:


Back in the days of analog recording 0 db was 1 volt. Since
this was analog the 0 db level could be and was often exceed.
With the advent of digital CDs the 0 db level became the
maximum level, which can not be exceeded because of the digital
format, and is supposed to be 2 volts. Since these are maximum
levels the average will much lower. Microphone levels are lower
and vary widely.

Not quite. Firstly, a dB is a relative level, not an absolute,
so without stating the reference, a figure of "xdB" is
meaningless. Originally, 0dB was referenced to a power of 1mW
into a load of 600 ohms, and was referred to as 0dBm. Later, the
same voltage level, but unloaded, that is, without reference to
a 600 ohm load became 0dBu (that is, unloaded) Note that the
voltage level is the same in both cases (0.775v, or 1mW into 600
ohm) There was a strange semi-standard evolved of referring to
1V rather than 0.775v and that was 0dBv.

Digital outputs are referred to maximum digital output (when all
the bits are 1) and that is called 0dBFS (0dB Full Scale). It
has NO analogue equivalent, as analogue can keep getting bigger
without limit, digital can't get any bigger than when all the
bits are 1. In Digital-Analogue conversion, a number of
different conversion levels have become more-or-less standard.
The EBU (European Broadcasting Union) have defined 0dBFS digital
to mean +18dBu analogue after conversion. The USA prefers that
0dBFS = +24dBu because that provides 20dB headroom above 0VU. A
few dissidents prefer +25dBu as that's 1dB better than
+24...........

CD players have evolved a standard output of 2v analogue for
0dBFS, but as far as I'm aware, there is no official standard
for this.


I can't say I understand all of what you write but the parts I do
understand are very useful to me. Thank you for posting.

Are there any web sites or documents which explain this sort of thing
for a beginner: rigorously but not going too fast.

Crossposting removed.

Hi,

"don" wrote in message
...
dbm is as stated a reference of two like power values to a 1mW reference
however the impedence does not need to be 600 ohms, it can be any value of
ohms as long as both power values are based on the same impedence

dbu is not unloaded but db(micro) it is as above but with a reference of
1microWatt it is not actually a u but the greek character mu

No, in this context it's dBu (note the capital B, for Bell). It's equally
valid to use a reference of 1 microWatt, but that's not what is used
commonly in professional audio. It might appear, for example, as
dB(?V/m) for electric field strength, relative to 1 microvolt per
metre. Not sure if the mu will come through in ASCII - apologies
if it doesn't.

If the load is 600 ohms, then dBu=dBm.

Regards,

Glenn.

"Glenn Booth" wrote in message
...
Crossposting removed.

Hi,

"don" wrote in message
...
dbm is as stated a reference of two like power values to a 1mW reference
however the impedence does not need to be 600 ohms, it can be any value
of
ohms as long as both power values are based on the same impedence

dbu is not unloaded but db(micro) it is as above but with a reference of
1microWatt it is not actually a u but the greek character mu

No, in this context it's dBu (note the capital B, for Bell). It's equally
valid to use a reference of 1 microWatt, but that's not what is used
commonly in professional audio. It might appear, for example, as
dB(?V/m) for electric field strength, relative to 1 microvolt per
metre. Not sure if the mu will come through in ASCII - apologies
if it doesn't.

If the load is 600 ohms, then dBu=dBm.

Regards,

Glenn.

Glenn is correct. dBu(micro)V is generally used for field strength
measurements and is referred to 1 microvolt/m.

dBu and dBm refer to the same *voltage* level, but different power levels.
dBm refers for 1mW into 600 ohms, dBu is the same voltage level (0.775v rms)
but without reference to a load. I have never heard of dBm being referred
to anything other than 1mW into 600 ohms, nor dBu being referred to 1 micro
watt. The point about dBu is that it is a *voltage* level reference, not a
power reference.

S.

On Sat, 18 Mar 2006 17:54:15 GMT, "don" wrote:

dbm is as stated a reference of two like power values to a 1mW reference
however the impedence does not need to be 600 ohms, it can be any value of
ohms as long as both power values are based on the same impedence


No, the impedance does not need to be the same, and there are not two
power values, but one - specified as dB with respect to one milliwatt.
Impedance does not appear anywhere in this figure.

dbu is not unloaded but db(micro) it is as above but with a reference of
1microWatt it is not actually a u but the greek character mu


dBu is indeed dB (unloaded). It is a relic of 600 ohm line audio
systems and is the voltage that would have produced 0dBm in 600 ohms,
but since we now run into high impedances instead, must be specified
otherwise - hence dBu.

dbv would be a ratio based on two voltage levels and a reference of 1 volt

dBV, actually, not dBv.

power db caclulations are 10 log Pout/Pin
Voltage db calculations are 20 log Vout/Vin

dbFS is "decibels full scale". It is an abbreviation for decibel amplitude
levels in digital systems which have a maximum available level (like PCM
encoding). 0 dBFS is assigned to the maximum possible level. There is still
the potential for ambiguity, since some use the RMS value of a full-scale
square wave for 0 dBFS, and some use a sine wave.

No, no ambiguity, dB below full scale does not depend on wave shape,
merely how many digital levels remain unused.

this is treated the same as voltag calculations because it is based on the
signal to noise ratio.

It has nothing to do with signal to noise ratio - it is all happening
at the other end of the scale.

d

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

"Don Pearce" wrote in message
...
On Sat, 18 Mar 2006 17:54:15 GMT, "don" wrote:

dbm is as stated a reference of two like power values to a 1mW reference
however the impedence does not need to be 600 ohms, it can be any value
of
ohms as long as both power values are based on the same impedence


Don,

Do you have a reference for this statement? In 34 years in Pro-Audio I have
never heard it expressed in this way, always referred to 1mW into 600 ohms.



dBu is indeed dB (unloaded). It is a relic of 600 ohm line audio
systems and is the voltage that would have produced 0dBm in 600 ohms,
but since we now run into high impedances instead, must be specified
otherwise - hence dBu.

dbv would be a ratio based on two voltage levels and a reference of 1 volt

dBV, actually, not dBv.


this is treated the same as voltag calculations because it is based on the
signal to noise ratio.

It has nothing to do with signal to noise ratio - it is all happening
at the other end of the scale.

I have no diea what the above is referring to: dBFS has nothing to do with
signal-to-noise, it is just how many dB below full-scale.

S.

On Sat, 18 Mar 2006 19:56:17 -0000, "Serge Auckland"
wrote:


"Don Pearce" wrote in message
...
On Sat, 18 Mar 2006 17:54:15 GMT, "don" wrote:

dbm is as stated a reference of two like power values to a 1mW reference
however the impedence does not need to be 600 ohms, it can be any value
of
ohms as long as both power values are based on the same impedence


Don,

Do you have a reference for this statement? In 34 years in Pro-Audio I have
never heard it expressed in this way, always referred to 1mW into 600 ohms.


No, it is just one milliwatt - no ohms needed. You have only come
across it in relation to 600 ohms because you have been worked in
audio, and that is all you have been exposed to. If you ever worked in
RF, you would have found exactly the same power, referred to in
exactly the same way in 50, 62.5 and 74 ohms. The power is the same in
all of these - and 600 ohms too.


dBu is indeed dB (unloaded). It is a relic of 600 ohm line audio
systems and is the voltage that would have produced 0dBm in 600 ohms,
but since we now run into high impedances instead, must be specified
otherwise - hence dBu.

dbv would be a ratio based on two voltage levels and a reference of 1 volt

dBV, actually, not dBv.


this is treated the same as voltag calculations because it is based on the
signal to noise ratio.

It has nothing to do with signal to noise ratio - it is all happening
at the other end of the scale.

I have no diea what the above is referring to: dBFS has nothing to do with
signal-to-noise, it is just how many dB below full-scale.

S.


Exactly.

d

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

Hi,

"Don Pearce" wrote in message
...
On Sat, 18 Mar 2006 19:56:17 -0000, "Serge Auckland"
wrote:


"Don Pearce" wrote in message
.. .
On Sat, 18 Mar 2006 17:54:15 GMT, "don" wrote:

dbm is as stated a reference of two like power values to a 1mW reference
however the impedence does not need to be 600 ohms, it can be any value
of
ohms as long as both power values are based on the same impedence


Don,

Do you have a reference for this statement? In 34 years in Pro-Audio I have
never heard it expressed in this way, always referred to 1mW into 600 ohms.


No, it is just one milliwatt - no ohms needed. You have only come
across it in relation to 600 ohms because you have been worked in
audio, and that is all you have been exposed to. If you ever worked in
RF, you would have found exactly the same power, referred to in
exactly the same way in 50, 62.5 and 74 ohms. The power is the same in
all of these - and 600 ohms too.

Agreed. We had the same conversation on uk.r.a back in 2003. I've
quoted a bit of it here as Serge might be interested:

I said:
I don't disagree that the reference must always be given, but for
measurements of power, such as those that reference dBm (dB referenced
to 1mW) surely the impedance is totally redundant? (Unless what one is
really trying to describe is voltage, but using a power ratio to do
so). The 50R says nothing that I can see about the power, it only
allows one to relate the voltage that will be dropped across that
particular impedance/resistance with that dB worth of power being
dissipated.

To which a certain Mr. Lesurf said this:

However, bear in mind two points:

1) That in most cases (in RF at least) the quoted systems will be based
upon assuming the system is impedance matched and then give the power that
will be delivered to the source. Hence quoting the impedance tells the user
that this is the required matched impedance for optimum power transfer.


2) That in most cases the receiver will tend to be designed to work over a
given voltage range due to finite voltage rails, etc. Hence the impedance
is useful for establishing the voltage levels that must be expected.


It is therefore useful to confirm the assumed impedances. In RF/microwave
we have the annoyance that 50 Ohm is common for system and lab work, but
other impedances like 75 Ohm, etc, crop up for specific purposes/areas.


In principle, though: yes, once you've quoted the signal power in dBm
you've established the power available. You could then use a transformer to
alter the impedance (and hence signal voltage) if so desired.


At the time, I hadn't considered case (1) that Jim pointed out, as I know

less than nothing about RF.

Who says Usenet doesn't go around in circles?

Regards,

Glenn.

"Glenn Booth" wrote in message
...
Hi,

"Don Pearce" wrote in message
...
On Sat, 18 Mar 2006 19:56:17 -0000, "Serge Auckland"
wrote:


"Don Pearce" wrote in message
. ..
On Sat, 18 Mar 2006 17:54:15 GMT, "don" wrote:

dbm is as stated a reference of two like power values to a 1mW
reference
however the impedence does not need to be 600 ohms, it can be any
value
of
ohms as long as both power values are based on the same impedence


Don,

Do you have a reference for this statement? In 34 years in Pro-Audio I
have
never heard it expressed in this way, always referred to 1mW into 600
ohms.


No, it is just one milliwatt - no ohms needed. You have only come
across it in relation to 600 ohms because you have been worked in
audio, and that is all you have been exposed to. If you ever worked in
RF, you would have found exactly the same power, referred to in
exactly the same way in 50, 62.5 and 74 ohms. The power is the same in
all of these - and 600 ohms too.

Agreed. We had the same conversation on uk.r.a back in 2003. I've
quoted a bit of it here as Serge might be interested:

I said:
I don't disagree that the reference must always be given, but for
measurements of power, such as those that reference dBm (dB referenced
to 1mW) surely the impedance is totally redundant? (Unless what one is
really trying to describe is voltage, but using a power ratio to do
so). The 50R says nothing that I can see about the power, it only
allows one to relate the voltage that will be dropped across that
particular impedance/resistance with that dB worth of power being
dissipated.

To which a certain Mr. Lesurf said this:

However, bear in mind two points:

1) That in most cases (in RF at least) the quoted systems will be based
upon assuming the system is impedance matched and then give the power that
will be delivered to the source. Hence quoting the impedance tells the
user
that this is the required matched impedance for optimum power transfer.


2) That in most cases the receiver will tend to be designed to work over a
given voltage range due to finite voltage rails, etc. Hence the impedance
is useful for establishing the voltage levels that must be expected.


It is therefore useful to confirm the assumed impedances. In RF/microwave
we have the annoyance that 50 Ohm is common for system and lab work, but
other impedances like 75 Ohm, etc, crop up for specific purposes/areas.


In principle, though: yes, once you've quoted the signal power in dBm
you've established the power available. You could then use a transformer
to
alter the impedance (and hence signal voltage) if so desired.


At the time, I hadn't considered case (1) that Jim pointed out, as I know

less than nothing about RF.

Who says Usenet doesn't go around in circles?

Regards,

Glenn.

Thanks to Don and Glenn. I've learnt something. Looking through my old
college texts books, I can see you're right. What comes of a narrow
upbringing.

S.