# What kind of an amplifier noise spec is this?



## Wayne A. Pflughaupt (Apr 13, 2006)

I’ve noticed that a lot of home theater receivers use a qualifier for their S/N ratio specs that I’m not familiar with. With pro audio gear, you’ll typically see something like “100 dB, A-weighted, below maximum output,” or “>95 dB, unweighted from 20Hz-20 kHz.” 

With home manufacturers like Yamaha, Onkyo, Rotel and a few others, the S/N rating is given as “xx dB, IHF A-Network.” 

What is that?

Googling “IHF A-Network” didn’t get anything meaningful. However, I found at the Rane Professional Audio Reference that the _“IHF (Institute of High Fidelity) is the old organization of North American hi-fi manufacturers that created voluntary industry standards for testing and specifying consumer electronics. The IHF merged with the EIA in 1979. Today the AES is responsible for setting audio standards in the United States._”

So – anyone here know what a noise spec qualified with “IHF A-Network” means? Can we assume that “A-Network” is the equivalent of A-weighting?

Regards,
Wayne


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## F1 fan (Jul 6, 2006)

I can't give you the answer Wayne but I can ask the R&D guys about it and see if they know.
I suspect it is similar to the A weighted measurement.


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## Danny (May 3, 2006)

I don't know what it means but it sounds to me like the manufacturers may be trying to spec their products with a different spec system to gain what seems to be a better rating. But hey I may be completely wrong


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## F1 fan (Jul 6, 2006)

It appears it is an A weighting spec.so it has filtering applied to better show the results in the mid band.

Danny, it probably does help the spec sheet by a few db compared to other methods.


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## Wayne A. Pflughaupt (Apr 13, 2006)

That appears to be correct, Fred. From RaneNote 15: Audio Specifications (note bold text):



> Pro audio equipment often lists an A-weighted noise spec -- not because it correlates well with our hearing -- but because it can "hide" nasty hum components that make for bad noise specs. _Always wonder if a manufacturer is hiding something when you see A-weighting specs._ While noise filters are entirely appropriate and even desired when measuring other types of noise, it is an abuse to use them to disguise equipment hum problems. A-weighting rolls off the low-end, thus reducing the most annoying 2nd and 3rd line harmonics by about 20 dB and 12 dB respectively. *Sometimes A-weighting can "improve" a noise spec by 10 dB.*


See also the sections on weighting filters and S/N (signal to noise ratio) from the excellent Rane Pro Audio Reference.

It's amazing how little info there is on this "IHF A-Network." I haven't had much luck posting this at AVS either.

Regards,
Wayne


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## khellandros66 (Jun 7, 2006)

Wayne thats an old school rating my dads old Magnavox stereo system is rated

100w RMS x 2 
150w x 2 IMP/IHF

This is a fancy way of saying Dynamic power.

~Bob


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## Otto (May 18, 2006)

khellandros66 said:


> Wayne thats an old school rating my dads old Magnavox stereo system is rated
> 
> 100w RMS x 2
> 150w x 2 IMP/IHF
> ...


Wayne asked about a noise spec, not power. 

The "P" in IMP _might_ have something to do with "peak", but I wouldn't necessarily assume that.

There is precious little out there on the web about IHF...


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## Otto (May 18, 2006)

If there's an AES member around here, s/he can download The Standards of the Institute of High Fidelity for $5. Still a steal for non-members of AES at the low price of $20. Assuming that IHF is an acronym for that apparently now-defunct group (and I think it is). I may keep searching to see if it's out there for free somewhere.

Or read page 19 here. They talk about IHF A-202 as a noise measurement standard in Onkyo Integra products.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Mystery solved by our own John M. Here's what he wrote on another thread:



> That is A-weighting, as set out in the (very) old IHF standard: THE INSTITUTE OF HIGH FIDELITY, INC. IHF Standard Methods of Measurement for Audio Amplifiers, IHF-A-202 (1966). It went through various revisions before being superceded by EIA-RS-490 (1981), which in turn has been superceded by CEA-490-A.


Regards,
Wayne


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## Sonnie (Apr 11, 2006)

I'm glad somebody understands it all... :scratch:


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