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Attenuator affects sound quality

post #1 of 12
12/20/07 at 10:08am
Thread Starter 
I sometimes use an attenuator (from UE) to get rid of a bit of hiss. Works great for the hiss but it affects the highs that are coming through. It kind of gets cut of a bit.

Anyone had similar experiences?
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post #2 of 12
12/20/07 at 10:18am
"Hiss" is in the higher harmonics. If you attenuate the hiss. You can decrease the upper register detail. What is your system in use? Why is there hiss? Is it analog tape? etc.
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post #3 of 12
12/20/07 at 10:32am
Thread Starter 
It's the (static) hiss from the amp/iPod when connecting a low-impedance headphone such as IEM. I'm using UE TripleFi's.
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post #4 of 12
12/20/07 at 10:39am
Quote:
Originally Posted by PaulK View Post
I sometimes use an attenuator (from UE) to get rid of a bit of hiss. Works great for the hiss but it affects the highs that are coming through. It kind of gets cut of a bit.

Anyone had similar experiences?
Yes, absolutely. I notice the same thing. Every time I use the attenuator from UE I notice sound quality degradation. I now just use it on the plane only, since it is more important to drop down the level to "acceptable" instead of "ear-piercing" levels, plus the quality of the audio in the plane is not that good to start with

Will
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post #5 of 12
12/20/07 at 10:58am
Is it possible to DIY a more audiophile quality attenuator? Of course it will never been as good as not having it there, but is there a way to make its presence and un-noticeable as possible?
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post #6 of 12
12/20/07 at 12:03pm
Un-noticeable - impossible, because the attenuator decreases damping factor dramatically. This is independent from the components used, just a mathematical fact. All you can achieve is noise reduction.
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post #7 of 12
12/20/07 at 1:04pm
hiss when using low-impedance phones that isn't heard when you use higher-impedance phones is, imho, the source or amp (whichever you're plugged into) misbehaving. It's literally the headphone driver circuit introducing noise because it doesn't handle low-z loads well.

But you'd have to have a 60-ohm or so headphone handy to know for sure, because adding ohmic resistance in the form of an attenuator or a cheap steel wire cable (I'm looking at you, Sennheiser) is going to attenuate some very high frequencies anyway.

As for DIYing a fancy attenuator, there are boutique resistors costing any amount of money you care to spend - but the noise characteristic differences between them can only be measured with extremely sensitive instrumentation and a lot of people will think you're barking mad if you claim to hear them.
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post #8 of 12
12/20/07 at 9:20pm
Quote:
Originally Posted by J.D.N View Post
Is it possible to DIY a more audiophile quality attenuator?
Absolutely. Instead of a plain series resistor (which is the most common way of doing this), it would have to be a voltage divider.

This is what you normally have:
Code:
     _____
o---|_____|---o        Rsource = R1
~      R1              Zload = Zhp + R1
o-------------o        (Vhp/Vout)nominal = Zhp,nom/(R1 + Zhp,nom)
and this is what you want:
Code:
     _____
o---|_____|-+-o
       R1   | 
            _          Rsource = R1 || R2 = (R1 * R2) / (R1 + R2)
           | |         Zload = R1 + (R2 || Zhp)
~       R2 | |                             (R2 || Zhp,nom) 
           |_|         (Vhp/Vout)nominal = ----------------------
            |                              (R1 + (R2 || Zhp,nom))
o-----------+-o
The problem with the simple series resistor is that it increases source impedance dramatically in order to achieve significant attenuation, which in turn means that the non-constant headphone impedance will distort the frequency response.

The voltage divider allows keeping a relatively low source impedance. This should be kept much below the nominal headphone impedance, a factor of 5 or 10 wouldn't be bad. Of course there are interactions with the attenuation and the impedance that the amplifier sees (I would avoid values under 16 ohms) - a low R2 means a high damping factor, but also implies that one has to trade off between amplifier loading and attenuation. In practice one has to find a tradeoff between all three parameters.

Assuming R1 + R2 = const, one could obviously also make an adjustable voltage divider with a single stereo pot by using all 3 connections, with better damping factor at lower levels.

Oh, and btw: The luxury version of an attenuator is an amplifier with an effective voltage gain of less than 1 - I would bet that no small number of portable amps is being used in this fashion.
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post #9 of 12
12/21/07 at 9:29am
Thread Starter 
The Shure attenuators can be adjusted. I don't have one... Do these follow this principle?
Any experiences on this one?
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post #10 of 12
12/21/07 at 9:51am
Quote:
Originally Posted by PaulK View Post
The Shure attenuators can be adjusted. I don't have one... Do these follow this principle?
Any experiences on this one?
The Shure attenuator is better than the UE one. You can plug it with max volume and get some hiss reduction with almost no SQ loss. As soon as you start playing with the volume knob of the attenuator you notice SQ reduction.
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post #11 of 12
5/25/08 at 8:07am
Quote:
Originally Posted by Bolardito View Post
The Shure attenuator is better than the UE one. You can plug it with max volume and get some hiss reduction with almost no SQ loss. As soon as you start playing with the volume knob of the attenuator you notice SQ reduction.
in that case, can i say that it is better to keep the attenuator at max vol while I stricly and only control the volume of my amp or source (depeding if im going amped or unamped) to retain high SQ?
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post #12 of 12
5/25/08 at 4:40pm
Head-Fi solution replace your attenuator with an amp.

Explorer
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