What does dBfs tell us

[asylum]

Hi all - puzzling question?
In the impulse window, what does the dbfs readout actually tell us about the room?
and what is the difference between it (dbfs) and the ETC dbfs graph,
so why would i choose one over the other?
do they tell us different acoustic events,
all help much appreciated.

[Sonnie]

I guess John Mulcahy will have to answer this one... I certainly have no idea.

[ludwignew]

Since you are not measuring voltage, the dBFS (Full Scale) tells the maximun point when a digital signal processor has its limits (due to the analogue-digital conversion and the system resolution ej. 16 bits, 24 bits, etc.). In other words, is the maximum value accepted in a digital measure.

The lowest possible sample is (for instance for 16 bit audio):
0000 0000 0000 0001, which equals -96 dBFS. Therefore the dynamic range for 16-bit systems is 96 dB. For 20-bit digital audio it is 120 dB. For 24 bit digital audio it is 144 dB.

[asylum]

Thank you, so looking at dbfs is only going to tell us level and nothing else in the impulse?

[JohnM]

The dbFS and % scales both show the amplitude of the impulse (or its ETC) but dbFS is a logarithmic scale whereas % is linear. When looking at the levels of reflections the % scale is usually more useful, when looking at decay times or choosing window settings dbFS is best.

[asylum]

Thanks for the explanation: in terms of looking at a rooms response, would i look at the dbfs in the ETC plot or the impulse plot, or do they both show the same information?

[JohnM]

The ETC shows the envelope of the impulse response, it is useful in % mode when looking at the level of reflections to assess the effectiveness of absorbers.

[asylum]

thanks john, what does the dbfs in ETC tell us? if in the impulse window it shows us decay?

[brucek]

what does the dbfs in ETC tell us?

Just as it says, Energy over Time.......

Very useful for looking at reflections and determining where they come from.

brucek

[asylum]

Oh i thought the db% was best for locating reflections... hmmmm, i guess i was wrong,
i am right in saying the dbfs in the impulse window will us decay time?

[asylum]

Hi Brucek

Very useful for looking at reflections and determining where they come from.

this is the view i should use not % for locating reflections?

[brucek]

this is the view i should use not % for locating reflections?

As John already pointed out above, it depends on what information you want - When looking at the levels of reflections the % scale is usually more useful, when looking at decay times or choosing window settings dbFS is best.

[asylum]

Thanks John and Brucek - It is all sinking in i promise,: and i,m putting my REW
education to good use, i,m getting used to taking measurments and now
comparing them, with and without absortion and carfully taking notes on
distances so i can learn what happens to the impulse graph.
thank you so much for all your help.