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ARSCLIST  September 2014

ARSCLIST September 2014

Subject:

Re: Distortion question

From:

DAVID BURNHAM <[log in to unmask]>

Reply-To:

DAVID BURNHAM <[log in to unmask]>

Date:

Tue, 30 Sep 2014 09:14:03 -0700

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (67 lines)

Any sound wave contains as much energy in the positive half as in the negative half, (otherwise the source of the sound, string, drumhead, whatever, would not come back to a rest point).  However the high frequency content of the positive half is much higher than in the negative half.  The best way to picture this is to capture a single wave of a complicated sound source and print this on a piece of paper.  If you have some way of measuring it, although the positive spikes will be higher than the negative spikes, the area enclosed in each half of the wave form, (say measured in square millimitres), will be identical.  This, as I think Tom said, is because brass and wind instruments are blown and blowing produces compressions of air which carry far more energy.  The subsequent rarefaction of air is caused by the air pressure recovering and returning to midpoint.  It is much easier to blow out the candles on a birthday cake than to suck them out. 
 Physicists will point out that every sound wave begins with a compression of air.  I have not experienced nor can I imagine why a trombone would have negative spikes.  The only explanation I can think of is that the absolute polarity of the microphone has been reversed, but that would affect trumpets as well.  As far as why a woman's voice would have higher spikes than a man's voice, my explanation, (which everybody is welcome to argue with), is that every human voice, male and female, has the same amount of high frequency energy - mainly consonants.  But a male voice has much more low frequency energy which might tend to mask some of the high frequencies, especially if he's close to a mike which might lop off the spikes.  Another interesting fact is that the frequency ranges of different instruments with their harmonic content vary only in the lower frequencies; the frequency range of a tuba's harmonics extends to the very highest audible frequencies 
 Years ago when rules were in place about the level of advertising compared to the level of the program, (I think advertising had to be 3 dB lower than the program - at least in Canada - at least at CBC), it was discovered that female voices had less energy but sounded louder so advertisers started using more female voices.

All of this, by the way, is why I believe that absolute phase or polarity of audio reproduction is so important.  The sound in the listening room should be in phase with the sound in the recording room.

db


On Tuesday, September 30, 2014 11:20 AM, Tom Fine <[log in to unmask]> wrote:
 


Brass plosives can be massive, and it is a dangerous undertaking to use condenser mics -- especially 
high-sensitivity vintage European condenser mics -- anywhere near loud brass instruments. In 
many-mic recordings, my father always used ribbon mics on brass. He did some testing in the 1950s 
and found that a muted trumpet could produce a blast of air that hit a U-47 hard enough to 
momentarily short out the capsule. Not to mention that vintage mics often ring, and condenser mics 
tend to ring in a way that brass blasts can trigger. And, brass blasts, especially trumpets and 
trombones, tend to occur within the "presence peak" frequencies of vintage condenser mics and can 
thus more easily overload a mic preamp.

-- Tom Fine

----- Original Message ----- 
From: "DAVID BURNHAM" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, September 30, 2014 11:09 AM
Subject: Re: [ARSCLIST] Distortion question


> As Lou points out, the distortion almost certainly occured in the mike preamp.  Trumpets and 
> Trombones, especially when muted, have a significantly larger positive excursion in the waveform 
> compared to the negative half, perhaps as much as 20 dB, (an announcer's voice exhibits the same 
> characteristic to a lesser degree).  A mike, (or an ear), placed close to brass often just snips 
> these spikes off but miked from a distance these spikes give the brass a presence which is very 
> attractive on orchestral recordings, big band recordings or even jazz solo recordings.
>
> db
>
>
> On Tuesday, September 30, 2014 10:07 AM, Bruce Whisler <[log in to unmask]> wrote:
>
>
>
> I am working with an old tape recording that has several instances of distortion that sound like 
> clipping.  When I view the waveform in my DAW, I see two things that are puzzling:
>
>
> 1.       The waveform in the distorted areas is not at a higher amplitude than other undistorted 
> sections.
>
> 2.       The waveform amplitude appears to be attenuated on the negative side of the waveform, but 
> not on the positive side.
>
> The distorted sections usually last only about a second and do coincide with loud high notes from 
> a trumpet soloist.  The recordings are from live performances in the 1970s.
>
> Any thoughts on what I am dealing with?  I have Izotope RX 3 Advanced, and have had little success 
> in repairing this particular problem with the Declip, Decrackle, or Declick modules.  I don't 
> think there is enough tone left under the distortion to effectively repair it.
>
> Thanks,
> Bruce Whisler
>
> 

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