[Fred McKenzie]

The auditorium stage is not perfectly flat so the conductor's podium
rocks. This results in an intermittent low frequency rumble throughout
a recent band concert recording.

I'm using Audacity to edit the recording. Audacity has numerous effects
including a high pass filter. I tried using that with a 10 Hz cutoff
and 24 dB per octave rolloff, but the rumble is still noticeable.

I would appreciate suggestions on a better approach to removing the
rumble from the recording. For example, using the High Pass Filter, how
high a cutoff frequency can I use without affecting the sound of
low-pitched instruments such as tubas and bass drums?

Fred

[Mike Rivers[_2_]]

On 6/13/2015 12:34 AM, Fred McKenzie wrote:
The auditorium stage is not perfectly flat so the conductor's podium
rocks. This results in an intermittent low frequency rumble throughout
a recent band concert recording.

It's hard to conceive of this. I wouldn't think that an unstable podium
would result in a low frequency rumble, but stranger things have happened.

I would appreciate suggestions on a better approach to removing the
rumble from the recording. For example, using the High Pass Filter, how
high a cutoff frequency can I use without affecting the sound of
low-pitched instruments such as tubas and bass drums?

First, you raise the cutoff frequency until the rumble is down to an
acceptable level. Then you listen to what you've left and decide if
you've done more harm than good. If there are only a few short periods
of the rumble, you needn't filter the entire recording, just the
segments that contain the rumble. That way you'll leave the full
bandwidth most of the time.

If it's a musical part that repeats, perhaps you can find a clean
version of that segment and edit it to replace the one with the
extraneous noise. Tedious? Yes. How important is it to save this recording?

Another possibility is to try a spectrum editor. I don't believe that
Audacity has one, but there may be have been a plug-in developed for it
since I last looked. iZotope is one of the better known companies that
makes a whole series of noise-reducing tools. The idea here is that
you're presented with a spectrogram view where amplitude is represented
by color and frequency is on the vertical axis.

As you play through the recording, and hear the noise that you want to
eliminate, you watch for it on the spectrogram - look for a bright
colored low frequency. "Lasso" it with your mouse cursor, click Delete
or reduce the level, and just that small chunk of frequency-in-time will
be affected. Of course if the rumble occurs simultaneously with a bass
note in the same frequency range, both will be gone, but generally there
will be harmonics of the musical notes that will come through so you'll
still have the sense that the instrument is there.

Any time you have a flaw in the recording, you have to decide on the
least offensive way you have available to clean it up, or just leave it
there and call it "organic" or "live."

--
For a good time, visit http://mikeriversaudio.wordpress.com

[Scott Dorsey]

Fred McKenzie wrote:
The auditorium stage is not perfectly flat so the conductor's podium
rocks. This results in an intermittent low frequency rumble throughout
a recent band concert recording.

I'm using Audacity to edit the recording. Audacity has numerous effects
including a high pass filter. I tried using that with a 10 Hz cutoff
and 24 dB per octave rolloff, but the rumble is still noticeable.

So, make it sharper, and bring it up higher. How high do you have to bring
it until the rumble is inaudible? The next step you take, then, depends on
how high that is. You may be able to low-cut the whole thing, you may have
to selectively low-cut only parts.

I would appreciate suggestions on a better approach to removing the
rumble from the recording. For example, using the High Pass Filter, how
high a cutoff frequency can I use without affecting the sound of
low-pitched instruments such as tubas and bass drums?

That depends on the piece and the instrumentation. You can probably make
it as high as 75 Hz without it being too serious a problem; there are bass
fundamentals lower than that but it might be better to lose them than to
have annoying podium noise. But you can do it selectively and leave some
parts out, if you have monitors that are good enough to let you know when
you're losing something.

If it's for broadcast, though, a low-cut at 100 Hz might be quite acceptable
even though you're going to be losing a lot of grunt on bass passages.

Next time check the podium and also check chairs for squeaks and if you
are using a moveable stage platform go over that for thumps and squeaks
too. And listen for the air conditioning noise; don't put your mikes
in line with strong AC or candle-induced air currents either.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Frank Stearns]

Mike Rivers writes:

On 6/13/2015 12:34 AM, Fred McKenzie wrote:
The auditorium stage is not perfectly flat so the conductor's podium
rocks. This results in an intermittent low frequency rumble throughout
a recent band concert recording.

It's hard to conceive of this. I wouldn't think that an unstable podium
would result in a low frequency rumble, but stranger things have happened.

I would appreciate suggestions on a better approach to removing the
rumble from the recording. For example, using the High Pass Filter, how
high a cutoff frequency can I use without affecting the sound of
low-pitched instruments such as tubas and bass drums?

First, you raise the cutoff frequency until the rumble is down to an
acceptable level. Then you listen to what you've left and decide if
you've done more harm than good. If there are only a few short periods
of the rumble, you needn't filter the entire recording, just the
segments that contain the rumble. That way you'll leave the full
bandwidth most of the time.

If it's a musical part that repeats, perhaps you can find a clean
version of that segment and edit it to replace the one with the
extraneous noise. Tedious? Yes. How important is it to save this recording?

Another possibility is to try a spectrum editor. I don't believe that
Audacity has one, but there may be have been a plug-in developed for it
since I last looked. iZotope is one of the better known companies that
makes a whole series of noise-reducing tools. The idea here is that
you're presented with a spectrogram view where amplitude is represented
by color and frequency is on the vertical axis.

As you play through the recording, and hear the noise that you want to
eliminate, you watch for it on the spectrogram - look for a bright
colored low frequency. "Lasso" it with your mouse cursor, click Delete
or reduce the level, and just that small chunk of frequency-in-time will
be affected. Of course if the rumble occurs simultaneously with a bass
note in the same frequency range, both will be gone, but generally there
will be harmonics of the musical notes that will come through so you'll
still have the sense that the instrument is there.

Any time you have a flaw in the recording, you have to decide on the
least offensive way you have available to clean it up, or just leave it
there and call it "organic" or "live."

What Mike said; I would only add that one of the boons of the digital era is the
ability to automate nearly everything including HP filters. So, you could move the
HP up and down -- move it up when the music got quieter and the noise was more
audible; then move it back down when more damage would be done to the music and at
the same time that louder music might mask the noise.

Also, understand that many people guess incorrectly about bass frequencies. Your
rumble is likely between 50 and 100 hz, with harmonics going way up from that,
perhaps well into the midrange. That is, you might do a 24 dB/octave HP to 1Khz,
make the music sound like it's through a telephone filter, and *still* readily
hear the noise. That's when you curse and swear.

Harmonics often do more to identify an unwanted noise of the type you describe than
you'd ever guess. There's the LF "whump" but that's not really what you hear when a
floor is being noisy -- is the higher-pitched resonance harmonics that give the
floor "whump" that sound.

My bread and butter is location recording, with all the accompanying issues of site
noise. I've had to do some interesting things, including the automated HP to
deal with severe HVAC rumble, and tuned narrow EQ notches to go after something.
And again, they're automated -- in and out before any noticeable damage is done.

I've seen some spectral EQ demos and have been intrigued, but haven't added one to
the kit yet.

Good luck with it.

Oh -- one last thought... at some point before the event walk the orchestra or band
area when the players are off stage and the house is empty and quiet. Look for
things that might make noise -- wobbly podiums and chairs, squeaky chair and stands,
etc.

Frank
Mobile Audio
--

[Fred McKenzie]

In article ,
Frank Stearns wrote:

Also, understand that many people guess incorrectly about bass frequencies.
Your
rumble is likely between 50 and 100 hz, with harmonics going way up from
that,
perhaps well into the midrange. That is, you might do a 24 dB/octave HP to
1Khz,
make the music sound like it's through a telephone filter, and *still*
readily
hear the noise.

Air handler noise is not normally a problem. Once the musicians played
a short piece on the auditorium floor, behind my microphones. I used
Audacity to greatly amplify the sound, which made air handler noise
obvious.

The "rumble" is more like a frequent "whump", not a continuous sound.
In previous concerts, the podium has been in slightly different
locations. At some concerts there has been noise, sometimes not.

I just tried using the high pass filter with a cutoff frequency of 50
Hz, 24 dB per octave rolloff. It made a noticeable improvement. Next I
will try the suggestion of raising the cutoff a little more and
increasing rolloff. If Audacity has a separate low cut effect, I did
not see it.

I did not hear the rumble on my computer's speaker. I had to burn a CD
in order to hear how it sounds on large speakers in another room. The
alternative of doing nothing may be a good idea!

Fred

[Fred McKenzie]

In article , Mike Rivers
wrote:

Any time you have a flaw in the recording, you have to decide on the
least offensive way you have available to clean it up, or just leave it
there and call it "organic" or "live."

I settled on Audacity's High Pass Filter set for a cutoff frequency of
55 Hz with 48 dB per octave rolloff. That took care of most of the
rumble. The few places where I can still hear it, easily fit into the
"organic" category.

I think the bass drum sounds are not quite as clean, but you can still
hear it. I do not think the Tuba was affected at all.

Thanks to all for the advice.

Fred

[JackA]

On Monday, June 15, 2015 at 2:06:00 PM UTC-4, Fred McKenzie wrote:
In article , Mike Rivers
wrote:

Any time you have a flaw in the recording, you have to decide on the
least offensive way you have available to clean it up, or just leave it
there and call it "organic" or "live."

I settled on Audacity's High Pass Filter set for a cutoff frequency of
55 Hz with 48 dB per octave rolloff. That took care of most of the
rumble. The few places where I can still hear it, easily fit into the
"organic" category.

I think the bass drum sounds are not quite as clean, but you can still
hear it. I do not think the Tuba was affected at all.

Thanks to all for the advice.

Not sure what people found interesting about that Rumble song. It utilized the techniques of distortion and feedback. See, that why we need superior sound quality to ensure we properly reproduce that distortion!!

Jack

Fred