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Amplifier THD
Amplifier THD
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Old 9th September 2021, 09:53 AM   #1
poundy is offline poundy  United Kingdom
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Amplifier THD
Default Amplifier THD

Is there going to be much actual audible difference between an amp that has a THD of 0.03% and one that 0.09%
I have read up on this and it says at 10% it tends to become audible


the amp i have just repaired ,the NAD 3030 has a spec of 0.09% but it sounds supurb, ive not ramped it right up yet (got to wait till the neighbours go out )

at realy low volume there is no distortion at all.
up against my current unit im using NAD 3240PE which i think is a realy good unit, it doesnt sound much different, if anything its a bit more mellow, a bit less 'bright'.



i think i have a good ear, i had them tested just over a year ago after i had an ear infection and according to what they told me after my ears are as good as a 25 years old, whch is suprising given the volume of noise they have put up with over the years
but is there much difference between 0.09% and 0.03%?
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Old 9th September 2021, 10:46 AM   #2
Mark Tillotson is offline Mark Tillotson
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0.03% is -70.5dB, 0.09% is 61dB, so a possibly detectable difference given the ear can sense
spurious tones at those levels below a carrier. But you need to chose careful test tones to make the difference audible in practice, such as 3kHz spur on 100Hz signal.

I've done some experiments and can detect a 7th harmonic of 100Hz if switched on and off abruptly down at -65dB, using headphones (speakers would probably mask this with their own distortion).

On general speech or music it would probably not be spottable, but most likely for electronic music which can resemble test tones at times (!).


Actually one case that can crop up in electronic music is two strong high frequency tones intermodulating (could even be ultrasonic), and the ear can be very able to spot a low frequency intermodulation product from these as the ear's sensitivity drops at HF to mask the originating tones, but is very sensitive to the lower freqeuncy of the product.

Last edited by Mark Tillotson; 9th September 2021 at 10:49 AM.
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Old 9th September 2021, 12:03 PM   #3
poundy is offline poundy  United Kingdom
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i always find things like some stringed instruments and particularly piano produces the most distorted sounds
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Old 9th September 2021, 12:23 PM   #4
jxdking is offline jxdking  China
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Quote:
Originally Posted by Mark Tillotson View Post
0.03% is -70.5dB, 0.09% is 61dB, so a possibly detectable difference given the ear can sense
That's also my experience.
For crossover distortion, 0.1% THD can be noticeable, if you play a pure sine wave tone.
With real music, usually I cannot tell.
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Old 9th September 2021, 01:21 PM   #5
wg_ski is offline wg_ski  United States
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Quote:
Originally Posted by poundy View Post
i always find things like some stringed instruments and particularly piano produces the most distorted sounds
Piano tends to be very revealing of IMD - because the spectrum is very rich. It’s not just the harmonic content - even when playing a single note there is more than one fundamental tone present. Think about it - the key hits multiple strings, all slightly stagger tuned. Then the sounding board has its own resonances that this tries to excite. Add intermods from the third thru infinity to this and it can sound anywhere from “fuzzy” to downright “staticky”. If your amp has too much crossover distortion, a piano will find it - even at much higher levels than the first watt. If you think an underbiased amp sounds bad with piano, try a class D amp with a long dead time. You’ll want to throw that one into orbit after 5 minutes with piano music.
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Old 9th September 2021, 02:46 PM   #6
haiqu is offline haiqu  Australia
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Amplifier THD
Quote:
Originally Posted by poundy View Post
i always find things like some stringed instruments and particularly piano produces the most distorted sounds
I pick it up mostly in choral works.
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Old 9th September 2021, 02:50 PM   #7
wg_ski is offline wg_ski  United States
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Same reason. The voices are not EXACTLY the same pitch, and even arrive at different times.
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Old 9th September 2021, 03:55 PM   #8
pwdiya12 is offline pwdiya12  United States
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A good working hypothesis is that an excellent studio microphone (say Nuemann U87- which could be used on piano or choir) can have a S/N ratio of about 80db- so I think that if the THD is around 0.01% and the THD+N is 0.02%, then these aspects will be inaudible. Consequently any amp designed for and meeting those specs is unlikely have any other audible distorting characteristics. on just my 2 cents/pence
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Old 9th September 2021, 05:02 PM   #9
WhiteDragon is offline WhiteDragon  United States
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Makes sense if comparing 2 different amplifiers with the same speakers.

More So
If you have a lot of hours of listening time on said speakers.

In a A / B quick listening test
Most wouldn't notice I would assume.

Interesting that the recording process got brought up.
Having done many recordings over the years.

I would say Piano and Drums rank the highest in most challenging to record.


Likewise the source recording can include more room sound or instrument sound
depending how the mics were placed.

When talking about the microphone, the mic preamp, limiter or compression
and the recording media. Especially analog tape.

Source recording is likely well over .03 or .09 distortion.


And even more curious if the thermal characteristic of the speakers would be more audible
Say the difference between 1 hour or 3 hours of heat in the voicecoils

Doing live sound with a few hours of continuous music
The Subs would get spongy sounding.
Very noticeable, since I had countless hours of listening
and very familiar with my speakers

Last edited by WhiteDragon; 9th September 2021 at 05:08 PM.
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Old 9th September 2021, 05:39 PM   #10
poundy is offline poundy  United Kingdom
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'what' determins THD % in an amp and what could be done in an amp with a poor THD to improve it without major work? or are we talking about a major design alteration?
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