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resonance at 500 Hz using headphones - maybe need a different DAC?

I'm primarily a headphone listener (Audeze LCD 2 pre-fazor) and I've been troubled by a resonance around 500 Hz that seems curiously dependent on my digital source. I'm looking to troubleshoot this resonance.

Note that all my equipment has modifications by a technician in the N.J. Audio Society. He adds bypass caps, damping, and ERS fabric.

I was using a modified iFi Nano for a while and liked it (with linear 5V power supply). Then I purchased a Gustard x20pro DAC, had the guy tweak it out. I noticed at first that the sound was much improved compared to my iFi Nano, in terms of an immediacy, transient power, dynamics (micro- and macro-), and so forth, but I was getting something undesirable, which was a resonance in my headphones on certain notes.

I have a musical keyboard and piano synthesis software on my MacBook, so I played different piano notes along with a spectrum analyzer plugin and a parametric EQ, and determined that the main resonance was happening at approx 500 Hz. (C above middle C). There was another resonance an octave above that.

This resonance is particularly noticeable on choral music.

Furthermore, I've made several improvements to my digital sound, like adding a better power cable to the Gustard, experimenting with an Aurender N100 music server, and experimenting with an iFi Zen Stream with different power supplies.

Whenever I tried something that improved the USB source (like adding a better power supply on the Zen Steam, putting a better power cord on the Aurender, etc.) the sound from the Gustard became even more immediate, involving, dynamic etc. But the more of this I was getting from the Gustard, the worse the resonance became. 

I tried two other DACs I had lying around. I went back to the iFi Nano. I also tried a Beringer 24/96 DAC from a long time ago (it's modified, runs off battery supply and is actually pretty good). Both of these DACs had much less resonance or maybe none. But they were less dynamic, transient speed, involving, etc. than the Gustard. Very dynamically tame compared to the Gustard and that's a bit disappointing were I to go with these DACs long term.

So I may want a new DAC if this is the fault of the Gustard, But that's what I'm trying to determine... could a resonance be related to some general good quality of a DAC, like transient speed? Or is a fault in the Gustard?

Before I decide that I want a new DAC, I just want to debug this resonance. If anyone has encountered something like it or has a theory where it comes from, I'd like to know.

magon
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o_holter
975 posts
 

A tone from an open string bass guitar, or guitar, tends to sound louder than a closed string further up the neck. Some DACs seem to give this fundamental sound more preeminence than others. But maybe not relevant for choir music ca 500 hz.

magon OP
41 posts
 

To address some of your comments:

Re: LCD-2: I don't think it's the headphone because it only happens on the Gustard. It doesn't happen on the modified iFi iDSD or the Beringer. Also it happens with another headphone, the AKG K712. And furthermore it's a very high-Q resonance. Very sharp, spans only about 3 half steps.

Re open strings: it is true that the 500 Hz resonance is triggered by notes with a lot of fundamental, because it's when the fundamental is at 500 hz (i.e. C above middle C) that it's loudest. It's much more noticeable on close-miked instruments. So for example an album by Maria Scheider, Walking By Moonlight, has a lot of close-miked instruments like piano and saxophone that move up and down scales and keep hitting the resonance. Whereas a chamber music album by Sheffield lab that has more of a perspective miking doesn't trigger the resonance much.

Bondmanp: so obviously you know were talking about Igor Kuznetsoff. He is still doing things from time to time and I'm in touch. I'm having him do one of his Dynamo power cords right now. I'll ask him if he can look at the Gustard. I was thinking I might solve this resonance by tweaking something, but at this point it's obvious I need the original expert to look at it.

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o_holter
975 posts
 

I have found that some DACs or systems emphasize the fundamental tones, more than others. As a test case I use Joe Cocker: Seven days, on his Sheffield steel album. This is a great track, with Sly and Robbie on drums and bass (if you want to define "tight", go here). You can really hear what bassist Robbie is doing, changing from the fundamental to the two upper chords in the three chord pattern (melody; Bob Dylan). When he goes up to a higher chord, the volume of the bass goes down. It is like Robbie takes a step back. Now the interesting point: this seems to vary, between my DACs. Two steps back, on some, just half a step on others. But I will need to test more. Just an impression.

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