[Randy Yates]

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.
--
Randy Yates % "Ticket to the moon, flight leaves here today
Digital Signal Labs % from Satellite 2"
% 'Ticket To The Moon'
http://www.digitalsignallabs.com % *Time*, Electric Light Orchestra

[Randy Yates]

Also, what reference level does an analog peak-reading meter
use?

--Randy

Randy Yates writes:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

--
Randy Yates % "She tells me that she likes me very much,
Digital Signal Labs % but when I try to touch, she makes it
% all too clear."
http://www.digitalsignallabs.com % 'Yours Truly, 2095', *Time*, ELO

[Randy Yates]

Cross-posting to comp.dsp.

--RY

Randy Yates writes:

Also, what reference level does an analog peak-reading meter
use?

--Randy

Randy Yates writes:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

--
Randy Yates % "Ticket to the moon, flight leaves here today
Digital Signal Labs % from Satellite 2"
% 'Ticket To The Moon'
http://www.digitalsignallabs.com % *Time*, Electric Light Orchestra

[rickman]

Since this seems to be a top posted thread and I don't like being
yelled at for top posting, maybe I shouldn't contribute... ;^)

I can't resist. I would not think by saying dBFS you are specifying
one way or another about whether a value is RMS or peak. The dB is
just a power measurement. Hmmm.... maybe I'm not thinking enough.
Because of the reference to meters, I am thinking of peak in the sense
of a vu meter that holds a peak value, not the peak level of an AC
signal. If you mean the latter, I expect all power measurements would
be RMS and dBFS is a power measurement, no?

Rick


On Nov 19, 5:09*pm, Randy Yates wrote:
Cross-posting to comp.dsp.

--RY



Randy Yates writes:
Also, what reference level does an analog peak-reading meter
use?

--Randy

Randy Yates writes:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

--
Randy Yates * * * * * * * * * * *% "Ticket to the moon, flight leaves here today
Digital Signal Labs * * * * * * *% *from Satellite 2"
* * * * *% 'Ticket To The Moon'http://www.digitalsignallabs.com% *Time*, Electric Light Orchestra

[glen herrmannsfeldt]

In comp.dsp rickman wrote:
Since this seems to be a top posted thread and I don't like being
yelled at for top posting, maybe I shouldn't contribute... ;^)

I can't resist. I would not think by saying dBFS you are specifying
one way or another about whether a value is RMS or peak. The dB is
just a power measurement. Hmmm.... maybe I'm not thinking enough.
Because of the reference to meters, I am thinking of peak in the sense
of a vu meter that holds a peak value, not the peak level of an AC
signal. If you mean the latter, I expect all power measurements would
be RMS and dBFS is a power measurement, no?

It does seem that the FS applies to measuring devices, either
analog or digital meters.

I believe, though, that it is usual to put a dB scale on peak-to-peak
reading VTVMs, with an assumed lead impedance and that the signal
is sinusoidal.

It seems to me that there is still some uncertainty in the
meaning of dBFS.

Well, consider that CDs are considered to have 96dB (or some
similar number) of dynamic range. That is comparing a full
scale signal (just about impossible in a live recording) to
one that is all quantization noise and no signal. That
doesn't seem quite fair.

-- glen

[Mike Rivers]

On 11/19/2010 5:36 PM, glen herrmannsfeldt wrote:

It seems to me that there is still some uncertainty in the
meaning of dBFS.

I think that's the only thing certain in this thread, but if
you're here from the comp.dsp crosspost, you may not have
encountered the concept.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[davew]

On Nov 19, 10:36*pm, glen herrmannsfeldt
wrote:
In comp.dsp rickman wrote:

Since this seems to be a top posted thread and I don't like being
yelled at for top posting, maybe I shouldn't contribute... ;^)
I can't resist. *I would not think by saying dBFS you are specifying
one way or another about whether a value is RMS or peak. *The dB is
just a power measurement. *Hmmm.... maybe I'm not thinking enough.
Because of the reference to meters, I am thinking of peak in the sense
of a vu meter that holds a peak value, not the peak level of an AC
signal. *If you mean the latter, I expect all power measurements would
be RMS and dBFS is a power measurement, no?

It does seem that the FS applies to measuring devices, either
analog or digital meters. *

I believe, though, that it is usual to put a dB scale on peak-to-peak
reading VTVMs, with an assumed lead impedance and that the signal
is sinusoidal. *

It seems to me that there is still some uncertainty in the
meaning of dBFS.

Well, consider that CDs are considered to have 96dB (or some
similar number) of dynamic range. *That is comparing a full
scale signal (just about impossible in a live recording) to
one that is all quantization noise and no signal. * That
doesn't seem quite fair.

-- glen

On digital audio meters we (the company I work for that is and many
others in the audio industry, I believe) use a dBFS scale and display
both peak spots (i.e. maximum absolute value latched for a set hold
time) and bargraphs with VU/PPM meter ballistics (neither of which are
RMS). The VU ballistic requires a 4dB hike to get over the "crest"
factor i.e. mean absolute (rectified) value is 2/pi. So a pure test
tone at any value will read/indicate the same level as the peak spot.
Of course, this does not apply to anything other than a pure test
tone.

So dBFS refers to peak sine wave level. 0dBFS is the largest level of
sine wave prior to clipping.

[Scott Dorsey]

glen herrmannsfeldt wrote:

It does seem that the FS applies to measuring devices, either
analog or digital meters.

NO. FS applies ONLY to digital system. When all the bits are set to 1,
the meter goes to FS.

It seems to me that there is still some uncertainty in the
meaning of dBFS.

Well, consider that CDs are considered to have 96dB (or some
similar number) of dynamic range. That is comparing a full
scale signal (just about impossible in a live recording) to
one that is all quantization noise and no signal. That
doesn't seem quite fair.

When all the bits are 1, the meter reads 0dBFS. When the bits are
all zero, the meter reads -96dBFS. It doesn't matter how difficult
or realistic it is to generate such a signal in the analogue world,
the measure is ONLY relevant for digital signals.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Peter Larsen[_3_]]

glen herrmannsfeldt wrote:

It seems to me that there is still some uncertainty in the
meaning of dBFS.

No. There are 10 kind of readers here, those that understand binary and
those that do not.

Well, consider that CDs are considered to have 96dB (or some
similar number) of dynamic range. That is comparing a full
scale signal (just about impossible in a live recording)

Oh no, what is difficult to some is to stay in the comfy -10 to -5 zone re.
FS instead of being at 0 dB FS for a number of consecutive samples.

-- glen'

Kind regards

Peter Larsen

[Al Clark]

0 dBFS is a digital specification that represents the maximum level that a
data converter can convert. For example 0x7FFFFF... or 0x800000.. assuming
twos complement.

It follows that the level of all signals will be = 0 dBFS

It has nothing to do with the rms level at all.

The relationship between nominal rms levels and dBFS is loose.
The more bits you assign for headroom, the less bits you have for low
levels.

A common professional audio tradeoff is 4dBu = -18dBFS. This would mean
that a +22dBu sine wave would just fit into the converter range without
clipping.

It is also common that 0dBu = -18dBFS. This means the maximum input level
is +18dBu.


Al Clark
www.danvillesignal.com




Rick


On Nov 19, 5:09*pm, Randy Yates wrote:
Cross-posting to comp.dsp.

--RY



Randy Yates writes:
Also, what reference level does an analog peak-reading meter
use?

--Randy

Randy Yates writes:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on
a
digital mixing console or a ProTools plugin), what units are
utilized?
I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

--
Randy Yates * * * * * * * * * * *% "Ticket to the m
oon, flight leaves here today
Digital Signal Labs * * * * * * *% *from Satellite 2"
* * * * *% 'Ticket To The Moon'http://w
ww.digitalsignallabs.com% *Time*, Electric Light Orchestra

[Randy Yates]

Al Clark writes:

0 dBFS is a digital specification that represents the maximum level that a
data converter can convert. For example 0x7FFFFF... or 0x800000.. assuming
twos complement.

It follows that the level of all signals will be = 0 dBFS

It has nothing to do with the rms level at all.

The relationship between nominal rms levels and dBFS is loose.
The more bits you assign for headroom, the less bits you have for low
levels.

A common professional audio tradeoff is 4dBu = -18dBFS. This would mean
that a +22dBu sine wave would just fit into the converter range without
clipping.

It is also common that 0dBu = -18dBFS. This means the maximum input level
is +18dBu.

Hey Al,

I'm trying hard to see an answer to my question in what you wrote and
failing.

Let me respond to you with this question: If you had a meter that
-24 dBFS with a Fs/4 sine wave, what would the peak value of the
sine wave be?

--Randy




Al Clark
www.danvillesignal.com




Rick


On Nov 19, 5:09Â*pm, Randy Yates wrote:
Cross-posting to comp.dsp.

--RY



Randy Yates writes:
Also, what reference level does an analog peak-reading meter
use?

--Randy

Randy Yates writes:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on
a
digital mixing console or a ProTools plugin), what units are
utilized?
I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

--
Randy Yates Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â*% "Ticket to the m
oon, flight leaves here today
Digital Signal Labs Â* Â* Â* Â* Â* Â* Â*% Â*from Satellite 2"
Â* Â* Â* Â* Â*% 'Ticket To The Moon'http://w
ww.digitalsignallabs.com% *Time*, Electric Light Orchestra



--
Randy Yates % "She has an IQ of 1001, she has a jumpsuit
Digital Signal Labs % on, and she's also a telephone."
%
http://www.digitalsignallabs.com % 'Yours Truly, 2095', *Time*, ELO

[Steve Pope]

Al Clark wrote:

0 dBFS is a digital specification that represents the maximum level that a
data converter can convert. For example 0x7FFFFF... or 0x800000.. assuming
twos complement.

It follows that the level of all signals will be = 0 dBFS

It has nothing to do with the rms level at all.

I woulda said that a 0 dBFS signal has the RMS level of a sine wave
that just barely doesn't clip a converter (or, a hardlimited channel;
it does not need to be a converter).

(This is an important concept, of sorts, in that is shows that
an N bit converter has a full-scale-signal to quantization noise
ratio of 6*N + 2 dB, not the 6*N + 5 dB that some texts claim.)

One can debate these things. Most outcomes of such debates are
equivalent within a factor of two.

Steve

[Randy Yates]

rickman writes:

Since this seems to be a top posted thread and I don't like being
yelled at for top posting, maybe I shouldn't contribute... ;^)

I can't resist. I would not think by saying dBFS you are specifying
one way or another about whether a value is RMS or peak.

I had the same impression until today when some very experienced people
on rec.audio.tech/rec.audio.pro informed me it was a peak measurement.

The dB is just a power measurement. Hmmm.... maybe I'm not thinking
enough.

I think you're thinking sufficiently, rick! In fact you're bringing
up a problem I hadn't even considered yet - how can you use dB for a
"peak" measurement when it isn't power? More about this below.

Because of the reference to meters, I am thinking of peak in the sense
of a vu meter that holds a peak value, not the peak level of an AC
signal.

At this point I am questioning everything myself, but my current
understanding of "peak" is the latter, or more precisely, the
maximum instantaneous level of a rectified AC signal. Usually
there is some sort of "reset" or "decay" so that it's sort of
a peak in a local temporal extent. See "Considerations for
accurate peak metering of digital audio signals", AES-R7-2006.

If you mean the latter, I expect all power measurements would be RMS
and dBFS is a power measurement, no?

Don't follow you here.

--Randy


Rick


On Nov 19, 5:09Â*pm, Randy Yates wrote:
Cross-posting to comp.dsp.

--RY



Randy Yates writes:
Also, what reference level does an analog peak-reading meter
use?

--Randy

Randy Yates writes:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

--
Randy Yates Â* Â* Â* Â* Â* Â* Â* Â* Â* Â* Â*% "Ticket to the moon, flight leaves here today
Digital Signal Labs Â* Â* Â* Â* Â* Â* Â*% Â*from Satellite 2"
Â* Â* Â* Â* Â*% 'Ticket To The Moon'http://www.digitalsignallabs.com% *Time*, Electric Light Orchestra


--
Randy Yates % "Remember the good old 1980's, when
Digital Signal Labs % things were so uncomplicated?"
% 'Ticket To The Moon'
http://www.digitalsignallabs.com % *Time*, Electric Light Orchestra

[Mike Rivers]

On 11/19/2010 7:28 PM, Randy Yates wrote:

you're bringing
up a problem I hadn't even considered yet - how can you use dB for a
"peak" measurement when it isn't power?

Easy . Because you WANT to.

At this point I am questioning everything myself, but my current
understanding of "peak" is the latter, or more precisely, the
maximum instantaneous level of a rectified AC signal.

Actually, it's the maximum voltage of the AC signal at the
peak portion of the waveform. It needs to be rectified in
order to be seen on an analog meter, but when you have an
A/D converter looking at the voltage every 1/44,100th of a
second (or whatever the sampling rate is) it's looking at
the absolute voltage, not an average, not one with all the
peaks going in the same direction. The converter needs to
convert negative peaks as well as positive ones.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Peter Larsen[_3_]]

Randy Yates wrote:

Also, what reference level does an analog peak-reading meter
use?

http://www.klay.com/klay/world_audio_levels.jpg

link supplied by Hank Alrich in some other context. Roger Orban made a
"multi-standard loudness meter" program some time ago, perhaps someone can
remember the download link, it is very illustrative.

--Randy

Kind regards

Peter Larsen

[Ken[_8_]]

On Sun, 21 Nov 2010 08:36:13 +0100, "Peter Larsen"
wrote:

Also, what reference level does an analog peak-reading meter
use?

http://www.klay.com/klay/world_audio_levels.jpg

link supplied by Hank Alrich in some other context. Roger Orban made
a "multi-standard loudness meter" program some time ago, perhaps
someone can remember the download link, it is very illustrative.


http://www.orban.com/meter/

[Mike Rivers]

On 11/19/2010 4:33 PM, Randy Yates wrote:

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

What, exactly, are you trying to do?

0 dBFS is a peak level. It can be only one sample long, and
you'll never come up with a useful RMS value for that. I
explained some instances where you'd know both the peak
level (full scale) and the RMS value of the waveform with
those peaks. But the two aren't really the same kind of
measurement.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Scott Dorsey]

In article , Randy Yates wrote:

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

That depends entirely on which averaging standard you decide to use.
Most common is LKFS according to ITU BS.1771 loudness standard. You
will never, never see this in the US, but RTW standalone meters can
display it.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Randy Yates]

(Scott Dorsey) writes:

In article , Randy Yates wrote:

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

That depends entirely on which averaging standard you decide to use.
Most common is LKFS according to ITU BS.1771 loudness standard. You
will never, never see this in the US, but RTW standalone meters can
display it.

Scott, sorry but I didn't see this until just today. Thanks. In
searching for info on BS.1771 I also found this paper from Grim Audio,
which, at a cursory glance, looks like it touches on many of the same
issues I've been asking about here.

http://www.grimmaudio.com/whitepaper...%20journal.pdf

--
Randy Yates % "With time with what you've learned,
Digital Signal Labs % they'll kiss the ground you walk
% upon."
http://www.digitalsignallabs.com % '21st Century Man', *Time*, ELO

[Scott Dorsey]

In article , Randy Yates wrote:
(Scott Dorsey) writes:

That depends entirely on which averaging standard you decide to use.
Most common is LKFS according to ITU BS.1771 loudness standard. You
will never, never see this in the US, but RTW standalone meters can
display it.

Scott, sorry but I didn't see this until just today. Thanks. In
searching for info on BS.1771 I also found this paper from Grim Audio,
which, at a cursory glance, looks like it touches on many of the same
issues I've been asking about here.

It seems like most of the messages I have sent, you haven't seen.

Let me reiterate he

If it says dBFS, it is a peak-reading meter that reads relative to the
highest digital value on the system.

If it is some kind of average reading meter, it is not reading dBFS, but
is reading something else. Because there are so many different standards
for average reading, precisely WHAT it is measuring can be hard to tell.

For example, the average meters on Pro Tools don't seem to match anything
else or meet any known standard. The ballistics are faster than VU.

If you actually need to have consistent and accurate average metering on
digital systems, you use BS.1771 metering. Most people don't, though.

Calling something RMS when it produces a weighted average is not correct.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Michael Dines[_2_]]

Scott Dorsey wrote:

For example, the average meters on Pro Tools don't seem to match anything
else or meet any known standard. The ballistics are faster than VU.

This answers something I've long wondered about - what do the meters on
the Pro Tools mix window measure when recording or playing back?

It's like the markings on the side of the waveform in the edit window -
are they meant to mean anything in dB? I've never foud anything in the
Pro Tools manuals to say what they're meant to mean.

[Mike Rivers]

On 11/23/2010 4:13 PM, Michael Dines wrote:

This answers something I've long wondered about - what do the meters on
the Pro Tools mix window measure when recording or playing back?

That there's audio there. They also give you an idea of how
close you're getting to clipping.

It's like the markings on the side of the waveform in the edit window -
are they meant to mean anything in dB? I've never foud anything in the
Pro Tools manuals to say what they're meant to mean.

I don't know about Pro Tools, but it's typical for waveform
graphics in a DAW to be scaled in dB, with the top and
bottom of the graph area representing full scale positive
and negative. This is the reason why everybody thinks his
mixes aren't "hot enough." With waveform peaks reaching a
fairly respectable -6 dBFS, the waveform fills only half the
area and looks pretty wimpy.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Don Pearce[_3_]]

On Fri, 19 Nov 2010 16:33:53 -0500, Randy Yates
wrote:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

dBFS answers the question "by how many dB must the signal be increased
for the highest peak to hit full scale"? I think that should answer it
for you.

d

[Randy Yates]

(Don Pearce) writes:

On Fri, 19 Nov 2010 16:33:53 -0500, Randy Yates
wrote:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

dBFS answers the question "by how many dB must the signal be increased
for the highest peak to hit full scale"? I think that should answer it
for you.

No.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized?
--
Randy Yates % "She has an IQ of 1001, she has a jumpsuit
Digital Signal Labs % on, and she's also a telephone."
%
http://www.digitalsignallabs.com % 'Yours Truly, 2095', *Time*, ELO

[Randy Yates]

Randy Yates writes:

(Don Pearce) writes:

On Fri, 19 Nov 2010 16:33:53 -0500, Randy Yates
wrote:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

dBFS answers the question "by how many dB must the signal be increased
for the highest peak to hit full scale"? I think that should answer it
for you.

No.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized?

Correction: change that i.e. to a e.g.
--
Randy Yates % "Ticket to the moon, flight leaves here today
Digital Signal Labs % from Satellite 2"
% 'Ticket To The Moon'
http://www.digitalsignallabs.com % *Time*, Electric Light Orchestra

[Scott Dorsey]

In article , Randy Yates wrote:

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized?

Correction: change that i.e. to a e.g.

As I said earlier, it depends entirely on what kind of "rms" measurement,
weighting, and ballistics you want. There is an IEC recommendation that
some people follow.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Mike Rivers]

On 11/19/2010 7:36 PM, Randy Yates wrote:

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized?

Oh! So what you're really asking is how does a program come
up with the level of a signal that's already in the digital
domain? Simple - however it wants, and it's usually wrong.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Don Pearce[_3_]]

On Fri, 19 Nov 2010 19:36:10 -0500, Randy Yates
wrote:

(Don Pearce) writes:

On Fri, 19 Nov 2010 16:33:53 -0500, Randy Yates
wrote:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

dBFS answers the question "by how many dB must the signal be increased
for the highest peak to hit full scale"? I think that should answer it
for you.

No.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized?

The problem here is mainly the general one of what an RMS measurement
means. With a sine wave it is easy. You can relate the RMS to the
peak, which in its turn relates to full scale - the only fixed point
with any significance in the digital domain.

With a music waveform that relationship does not exist in any
meaningful way. The only ratio of any practical use is how many dB
short of full scale is the largest peak - dBFS in other words. And it
isn't a matter of dynamics as in a PPM - it is simply a
sample-by-sample assessment. "Have I hit full scale or not?". Of
course digital console must be used by people who are accustomed to
the analogue domain, and want metering that works in the fashion they
are used to. This means the compromise of the PPM or VU meter, which
never provides that one vital piece of information.

As for making an RMS measurement, of course you can always use the
units of volts by relating it back to the ADC or forwards to the DAC.

d

[Randy Yates]

(Don Pearce) writes:

On Fri, 19 Nov 2010 16:33:53 -0500, Randy Yates
wrote:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

dBFS answers the question "by how many dB must the signal be increased
for the highest peak to hit full scale"? I think that should answer it
for you.

That does answer the question of what you think dBFS means. Although
that wasn't my question here, it is useful - thanks Don.
--
Randy Yates % "She has an IQ of 1001, she has a jumpsuit
Digital Signal Labs % on, and she's also a telephone."
%
http://www.digitalsignallabs.com % 'Yours Truly, 2095', *Time*, ELO

[Ian Bell[_2_]]

Randy Yates wrote:
Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.


dBFS is NOT a measurement method (peak or rms) but a specification for a signal
level. Unlike dBm, dBu and dBV is has NO SPECIFIC PHYSICAL VALUE - it is simply
the largest value that a digital system can represent.

Cheers

ian

[Mike Rivers]

On 11/20/2010 6:16 PM, Ian Bell wrote:

dBFS is NOT a measurement method (peak or rms) but a
specification for a signal level. Unlike dBm, dBu and dBV is
has NO SPECIFIC PHYSICAL VALUE - it is simply the largest
value that a digital system can represent.

That's one way of looking at it. The other way of looking at
it is that when you know the relationship between full scale
and output level or input sensitivity, dBFS has a physical
meaning. However, it's more useful to specify a voltage (dBu
etc.) than dBFS when working with actual useful digital
audio hardware.

I've been trying to find out what the original poster's real
question is, but he seems to either not be sure or just
refuses to answer, rather enjoying saying "no, that's not
it" rather than formulate a question that isn't abstract.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Ian Bell[_2_]]

Mike Rivers wrote:
On 11/20/2010 6:16 PM, Ian Bell wrote:

dBFS is NOT a measurement method (peak or rms) but a
specification for a signal level. Unlike dBm, dBu and dBV is
has NO SPECIFIC PHYSICAL VALUE - it is simply the largest
value that a digital system can represent.

That's one way of looking at it. The other way of looking at it is that
when you know the relationship between full scale and output level or
input sensitivity, dBFS has a physical meaning. However, it's more
useful to specify a voltage (dBu etc.) than dBFS when working with
actual useful digital audio hardware.

I've been trying to find out what the original poster's real question
is, but he seems to either not be sure or just refuses to answer, rather
enjoying saying "no, that's not it" rather than formulate a question
that isn't abstract.




He is also getting confused between the definition of signal level (like dBu for
example) and the means of measuring a signal level like RMS or peak.

Cheers

Ian

[Ben Bradley[_2_]]

On Fri, 19 Nov 2010 16:33:53 -0500, Randy Yates
wrote:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

What an interesting thread. It's funny the things that get argued
again and again ... good to see that Usenet is still alive!

My answer is that dBFS is a peak measurement (and most likely of
samples, not of a reconstructed waveform, which could be higher) as
displayed by the bargraph "meters" in most recording software, unless
it says it's something else. The something else is usually RMS.

There's been debate in this thread about bits vs. voltages (or
power, which is the "root" (sorry) of the RMS voltage measurement). I
really see no conflict here. The dB levels calculated with bits (more
specifically, linear PCM representations of discrete sampled voltages)
are the same as when the samples are put out through DAC's and the
relative voltages measured and the dB values calculated from those.
The numeric values are just binary representations of voltages, and
the values are calculated the same way. The dB value is the ratio of
two values of power, or two values of RMS voltage into a fixed
resistor, or between two sets of samples whose RMS values are
calculated.

This reminds me of a thread I read here (rec.audio.pro) long ago on
dBFS RMS measurement, and how one recording program did it.

First is a setup thread, "The Crest of the Wave (reference stuff!):"

http://groups.google.com/group/rec.a...213daf805e93c9

Next, the thread I remember: "RMS in CEP, just in from Syntrillium"
(that's Cool Edit Pro, presumably used the same RMS code as Cool Edit
96, both by Syntrillium before Adobe bought it all and renamed it
Audition):

http://groups.google.com/group/alt.a...cacf7552df88d7

I hope that sheds more light than heat. It's also notable that
there are several participants in those 11-year-old threads that are
also posting in this one.