[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Acoustics==>reverberation time
From: |
Gary Nelson |
Subject: |
Re: Acoustics==>reverberation time |
Date: |
Sat, 4 Dec 2010 11:00:12 -0600 |
I use Audacity to make RT-60 measurements using a good quality condenser
microphone. The details of making the recording would be a separate topic.
Microphone placement affects the results. You probably want to know this
information for humans to sit and listen to something, so put the mike at ear
level. An omnidirectional microphone is preferable to a cardoid at least for
first cut results.
Get some large toy balloons and inflate a couple as full as possible. Start the
recording with Audacity.
Pop a balloon and wait a few seconds and stop the recording. Location of the
pop also affects results. On stage is a good place as that is source of live
music for example. See method for using speaker(s) below.
Now select a pulldown menu on the track and choose "waveform in dB." Tho
balloon pop approximates an acoustic impulse, so the recording approximates the
impluse response of the space at the location of the microphone. In
Edit/Preferences set the output format range to 60dB. The display will look
like an arrow. Normalize the recording so that the peak is at zero dB. Now when
the signal decays to - 60dB, the time from onset to that point is the
Reverberation Time to -60dB aka RT60. You may find that the background noise
in the room is above -60dB so the RT has to estimated by using a straight edge
to extrapolate the decay down to -60.
Another way to excite the room is to generate a signal using Audacity's pink
noise generator at a level near maximum (like .9) and make a pulse a few
seconds duration (longer that the RT-60).
Play the sound pulse and record the result. You will see the excitation and the
recording. The recording will show a rise to equalibrium/steady state, flight
time delay (from the speaker to the mike -- estimate distance in feet from
speaker to mike -- sound travels 1100 ft/sec -- I use 1ms/ft as a way to get a
quick estimate), and then the arrow as the signal decays to -60dB.
For example, if the speaker is 50 feet from the mike, it will take most of 50
ms for the sound to travel from the speaker to the mike. You will see the
excitation pulse end and about 50ms later the recorded signal will begin to
decay.
Pink noise is white noise that has been filtered to decay at 6dB per octave --
also known as 1/f noise. Most sound from natural sources has this 1/f quality
so it is a decent excitation signal.
Audacity also offers a fourier transform tool. It is useful to apply the FFT
tool to the steady state recordiing and look at results. If the room has
resonance(s), they will be visible as peaks in the spectrum.
Gary Nelson, PhD
address@hidden
On Nov 21, 2010, at 4:11 AM, Martin Maxino wrote:
>
> Can i use Octave for acoustical measurements like Reverberation Time, etc.
> --
> View this message in context:
> http://octave.1599824.n4.nabble.com/Acoustics-tp3052251p3052251.html
> Sent from the Octave - General mailing list archive at Nabble.com.
> _______________________________________________
> Help-octave mailing list
> address@hidden
> https://www-old.cae.wisc.edu/mailman/listinfo/help-octave
>
[Prev in Thread] |
Current Thread |
[Next in Thread] |
- Re: Acoustics==>reverberation time,
Gary Nelson <=