Strange "flapping sound" audio distorion

May I suggest you start at the beginning ? No-one's heard your wav file.

What happened ?

What do you mean by a " more modern program " etc....... ?

Graham

========================================= Could it be "motor-boating" in the audio amplifier?

Motor boating is due to very low frequency positive feedback between output and low-level amplifier stages via the DC power supply. It results in a sub-audio frequency oscillation which cannot be heard from the loudspeaker but amplifier gain varies in sympathy with the oscillation frequency.

It can be remedied by improving decoupling of the low-level stages from the power supply.

But it may be a defect in the DC power unit which has an abnormally high internal impedance. This allows the power amplifier stage to develop signal-related voltages across the power supply which are fed back to earlier amplifier stages. Or it may be fed back to the other half of the sterio amplifier which shares the same DC power supply.

This is a case of very careful listening with a pair of ears, and an understanding of what might be going on, being a better diagnostic tool than a whole collection of electrical measuring instruments.

On the other hand, the distortion may be nothing to do with motor boating. Describe the symptoms more carefully.

You could connect a 10,000 or 20,000 microfarads capacitor across the DC power supply and see what happens.

Has the distortion always been there, or did it suddenly appear?

You reckon he has a valve/toob amplifier ?

Graham

=======================================

Motor boating can occur just as easily in transistor amplifiers.

Not typically. Few transistor amplifers are designed that badly ( especially wrt a single supply rail ).

Graham

========================================= On the other hand, few 'toob' amplifiers are designed that badly. Like transistor amplifiers they should never get out of the laboratory.

How many amps are designed so that they don't behave badly with failed components? The only motor-boating amp I heard was a Grundig in nineteen sixty-something. When it was repaired (not redesigned) it worked again.

I've got about 3 seperate brands of transitro radio that will motorboatr at low battery voltage.

The flapping sound might be a subsonic tone that was use for remote controlling some equipment.

You can get rid of some of it with a sharp cut-off high pass filter, but if it was distorted along the way, the distortion overlays your narration and is harder to get rid of.

You might be able to get rid of the harmonics with a bank of notch filters.

Adobe Audition has a lot of good tools for dealing with situationsl ike this.

I reckon the 'transistor radio' is hardly the pinnacle of modern design !

I imagine that's where the battery goes hi-Z.

Graham

It is very popular in old 1970s gear... electrolytic caps dry out and the bass poles and zeros start moving around. Sometimes they wind up in bad places.

--scott

"Ben Markson" wrote in news:IC_Cf.2764 $J81.1911@trndny01:

Simple noise at about 120 Hz and below can sound like that if it's loud enough. Sounds like the buffeting you hear when driving in a car at high speed with the windows open.

The only solution I've found is to filter it out anytime the bass isn't covering it (i.e. during narration and commenting). Tedious but effective.

I'm shocked. Shocked I tell you. A radio I bought for the price of 4 loaves of bread being not the pinnacle of modern design, it's going back :)

Basically, I'd imagine.

In article , Pooh Bear wrote: [...]

Do you mean the number of designs is low or the number of units produced is low? I can believe that very few crappy designs get generated but not that they wouldn't be mass produced if they cost less.

The AM-FM radio in my 1977 Dodge Omni was mass produced and was a good argument against the quality of transistor amplifiers, transistor radios, plastic knobs, sheet metal screws, angle brackets, connectors, chassis bending and cars that transistor stuff can be bolted into.

Yet there was, inexplicably, a Carroll Shelby Omni...

-- Les Cargill

Let's hear it then. Else we're just guessing. Post a sample on a web page.

Hard to tell without listening to it. One possibility is your recording device has some sort of automatic level control, which when hit with speech is bringing up the background noise level between words. Once this has been recorded there's no easy way to get it out.