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Old 29th November 2010, 12:06 PM   #1
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Default Motional/active feedback in the car?

While out driving the other day, I was endlessly fiddling with the tone controls and the problem was that conditions would change, such as speed, wind, road noise, engine, etc. . . This would cause the audio system to wander between shouty or muffled and I don't like either.

So howabout something like a microphone arrangement within the negative feedback loop of an op-amp, serving as a small preamplifier. . . enough motional/active feedback to knock the edge off?

I'm not exactly sure what device I'm asking for, so could somebody interpret?

Thanks!
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Old 29th November 2010, 02:11 PM   #2
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What you are describing is a "NOALA": noise operated automatic loudnes ampplifier.
Alted 1605A, Symetrix 571/2, Peavey GAP etc.
These products are used in airports, arenas, shoppingmalls etc to change paging level automatically.
These are sophisticated devices. The amplified sound from the speakers has to be subtracted from the ambient noise before gain control. With a paging system (even with Muzak on) that is easy as the sampling microphone can take samples and average between pages. With continuous music in HiFi .....
E
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Old 29th November 2010, 05:11 PM   #3
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Howabout noise operated automatic tone control?
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Old 29th November 2010, 06:44 PM   #4
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An example of the problem with radio. . . the car only makes this worse. . . but radio sound does have AGC/Compressor/Limiter to have a station sound as loud as its competition. If a station didn't have that, it would be hard to detect its existance when tuning across the radio dial.

However, the problem is that the presence or lack of bass determines the output volume, whereby tracks without as much bass will play the voice band much, much louder.

Here's a decent radio station type processor, $0, fits Winamp and also works with Foobar if you team it up with the Winamp to Foobar bridge (foobar's site has it). The top bar of the Enhancer program is AGC, the Boost is apparently a compressor. Harmonic bass is like dbx 120a, and it also has the next octave up for balance. Harmonic treble is something I can't figure out what is, but it helps compensate for the Ambiance, which is a reverb control.
Here's the link
Enhancer 017 - Winamp

To cause the radio station effect, lower the player's own volume control to 1/3rd or less and then click (turn on) the boost feature. Now, Enhancer's AGC will do radio sound, capable of maximizing the output of either a radio transmitter or a pa system.

Doesn't require a radio:
The free processor will even cause a little 25 watt per channel amplifier to crack plaster in sincere imitation of a big dance club.

So, if you play with that enhancer software, you'll notice that the AGC cranks up much higher during voice-only playback AND for music tracks that don't have as much bass on the original recording. The car radio doesn't have any circuits aboard to cancel out this effect, which is a rather painful problem. So, we could look at that problem instead of road noise.

Its probably possible to get the job done without a microphone. Maybe a mild, slow agc that's deaf at bass, mid-bass and high-treble, so that its only an automatic de-shout control? In other words, AGC only the ear's most sensitive frequencies by a few db? That could really help in the car.
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Old 30th November 2010, 11:51 AM   #5
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That software will demonstrate the distortion, so what device is needed to cause cancellation at the receiver?
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