Do you hear it even at lower volume levels? Might be on the recordings. A lot of sixties-era jazz recordings seem to go into overload on piano.
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I think it may be your amplifier 'clipping' as it runs out of power? The piano is one of the most dynamic of all musical instruments and the differences between ppp and fff are just about the greatest dynamic shift you can get in a recording.
You didn't seem to answer Drubin's question about it occurring at very low volume? If the distortion is still there at very low volumes, then it is NOT the amplifier clipping.
The Halcro outputs over 300 watts into 4 ohms. Your speakers are rated 90 db sensitive with a 6 ohm nominal and 3.8 ohm minimum impedance. Things look pretty good on the power amp/speaker side of things.
You might be overdriving the input to your Classe processor. Your statement that "perhaps less obvious with RCA ICs than with XLRs" supports this, since the balanced connections are 6db louder than the unbalanced. I note that the NAD has a maximum output of 4.2 volts balanced while the Classe maximum input rating is 3.6 volts.
Food for thought.
I also experience this with Fourplay's CD "Heartfelt" track no. 6. I often listen to music at moderate to high volume levels and got panicked when a few notes on the piano at a given passage got out of tune and distorted. I thought the speakers' drivers were blown or something but knew it was the recording as the defect remained when the the tune was played at low volume levels.
I would be glad if anybody who has this Fourplay "Heartfelt" CD can confirm on this. I suspect the recording engineer has screwed up on that particular part.
Thanks for all the food for thought, gang.
I should have mentioned I did listen some through headphones with my previous processor (Anthem AVM-20) and got the fuzz clearly then too, so since then I have been assuming that the speakers and their cables are unlikely to be the culprits. As I mentioned, the amp has been changed (and someone noted, the Halcro has lots of power in reserve) so it never seemed like that was the issue.
To (partially) summarize your other suggestions:
1. the recordings themselves. Piano does seem to be the toughest thing to get without distortion, and the increases I've made in fidelity with upgraded gear may bring it out more. If so, then c'est la vie, I guess :)
2. a voltage mismatch/overload between the NAD (maximum output of 4.2 volts balanced) and the processors-- although the Anthem is rated at 5.3 Max input.... This is a new area to me-- Is there anything to be done about something like that, short of getting a new player?
It's not a big enough drag to kill the pleasure I'm taking in this system-- just trying to learn more about the many mysteries of audio...
Your "loudest" "most intense attack" and mid-frequency observations suggest that this might be overloaded mikes on a close miked recording. IME, you usually tend to hear this as hardness in the presence region or (possibly) distortion in the bass, but if you really screw it up, I guess you can get distortion even that high up. Recording piano is a bitch.
BTW, if the piano goes "hard" (i.e., a grand begins to sound like an upright or a new upright begins to sound like an old upright) in this range before the distortion sets in, it's fairly likely that the recording is your problem.
Ryder, I listened to the Heartfelt Cd today and found no traces of piano distortion. It may be possible you have a faulty one. Though, it may be possible I have faulty ears!
I do have the "Grand Piano Canyon" lp by Bob James that has most of side 2 being defective where only the left channel plays correctly. The right channel plays at a much lower volume, and, if I remember correctly, is very distorted. Haven't played it in a long time.
Abucktwoeighty, thank you for your response. Your ears are fine. In fact, it was my mistake to make that comment without covering all bases. On that particular night of listening session, the amp was powered up for 1 hour from cold. Apparently the warm-up time on the amp was insufficient. I've listened to the recording again yesterday full-blast with the amp left on for 24 hours and the vibration/distortion on the piano keys starting somewhere in the passage from 2.17 to 3.12 is gone, completely.
Looks like it's not the recording or faulty speakers but the insufficient warm-up time on the power amp. I apologize for the confusion without analyzing on all aspects. I somehow knew Fourplay's recordings are of high quality and something must be amiss for them to exhibit this kind of flaw. At least now I know the amp needs to be on standby mode for a much longer period before it is able to perform on its optimum.