Hi George,
From my technically limited layman’ s perspective, the quote you posted from Optoma USA actually seemed logical and made some sense to me. If I didn’t know better from years of personal experience, I’d probably just accept what they stated as the truth, assuming they knew what they were talking about.
However, I find myself still resisting this theory that current class D switching frequencies cause sonic artifacts/anomalies in the audible range for several main reasons:
1.Two well credentialed and well respected amp designers whom I also respect and trust, atmasphere and Bruno Putzeys, have made statements that there’s no need to raise the switching frequencies for class D amps from the current mid-500kHz to the 3-5 mHz range.
2. If these proposed sonic artifacts/anomalies and supposed phase shifts actually do negatively affect the sound quality as theorized, I would think that a certain percentage of the currently thousands (millions?) of class D amp users, including myself, would be capable of detecting any peculiarities in the sound quality in their systems. I would also expect a certain portion of these users would be alarmed enough to post their observations on this or other audio forums seeking explanations and advice.
Oddly, the only comments I’ve read questioning the sound fidelity of class D amps were made by you, George.
To be fair, I have read comments by others claiming that they thought class D amps sounded cold and sterile but I’m not sure if these perceptions are related to sonic artifacts. I always made sense of these comments by questioning the quality of the class D amp they heard. After using 3 different class D amps from 3 different companies for soon to be the past 3 years, I’ve never perceived any of them to be cold and sterile and have never heard anything I would classify as a lack of fidelity.
I’ve asked you numerous times whether you’ve ever personally heard these elusive,quiet and apparently very difficult to notice sonic artifacts from a class D amp and if you could describe what they actually sound like but you never responded.
I wanted to keep an open mind and know what to listen for when I actually spent a couple hours listening to some very familiar music trying to be hyper-critical and detect anything that didn’t sound quite right. I didn’t hear anything amiss.
3. There seems to be a serious lack of any scientific studies or research concerning the affects that particular switching frequency ranges utilized in class D may have on the the actual audible musical signal frequencies being amplified. I’m referring to carefully controlled tests and experiments, with the results required to be consistently and reliably achieved when conducted by independent scientists before results can be verified, conclusions reached and a knowledge base on the subject can begin to be established.
The absence of a solid knowledge base allows individuals such as yourself, George, to put forth any theory that serves their purposes without being constrained by anything as silly as needing to support their theory with actual evidence such as facts or at least agreed upon truths.
But enough of this scientific mumbo jumbo, the simple truth is that I would have sent back my first class D amp for a ’no questions asked’ full refund, and bought a more expensive traditional linear amp, if any of these theorized sonic artifacts or phase shifts caused an audible lack of fidelity in any part of the audio spectrum.
The only thing I heard was a small, lightweight, efficient/electricity sipping, cool running, $630 Class D Audio SDS-440-CS class D amp significantly outperforming my large, heavy, inefficient/electricity gulping, hot running, $2,400 former Aragon 4004 MKII class A/B amp in almost every amp criteria that I care about: much better bass response, a much lower noise floor, better dynamic range and a much more neutral and detailed presentation. Both amps had a roughly equal ability to present a solid, stable and realistic 3D sound stage illusion while both had similarly very good mid-ranges and trebles that were well extended but not fatiguing.
Tim
