I happen to agree with his view on a hashkafic level. If you believe listening to recorded music during sefirah is assur at all, what difference does it make which instrument, the human voice or trumpet, is making the music. Also, he mistranslated a capella.The problem I have in understanding this logic is based on the distinctions Rav Belsky makes between different kinds of acapella music. If he'd assert that all acapella music recordings are forbidden, it'd be consistent, it seems to me. (It'd still be a hashkafic as opposed to halachik argument.) As it is, although I kind of have a sense of what he's opposed to (I think), his distinctions seem arbitrary.
For instance, with regard to EQ (since he specifically mentions it being a problem). What about proximity effect on microphones? By getting closer to most mics during recording, the vocalist increases the bass frequencies beyond what the ear would typically perceive the voice's frequency range to be. How far from the mic does a vocalist have to stand for the resultant recording to be permissible? Presumably there would be a different distance for each mic depending on its frequency response, the recording space, etc. How would Rabbi Belsky address this issue? Do we need a rav hamachshir on mics issuing the "Complete Guide to Sefirah Mic techniques" specifying acceptable distances for each of the commonly used vocal recording mics?
In short, without a clear understanding of the recording process (something it is evident Rav Belsky does not have based on the descriptions in this article), and without sources, it seems like Rav Belsky is trying to quantify a highly subjective feeling without accurate information. I suppose that's an approach for deciding one's personal beliefs, and for those who look to Rav Belsky for hashkafic advice, kol hakavod for following your rav's guidance. However, publishing this without sources as a normative halachik ruling in a newspaper seems anti-intellectual to me.
In the old days, the halachik process used to work by Rabbonim writing sourced teshuvos explaining their opinions. Over time, through point and counterpoint in writing (and/or in publivc presentations), with sources and logic that could be studied and reviewed, a halachik consensus often emerged (e.g. using electricity on Shabbos). Even in situations where no halachik consensus was reached, the sources and rationale for the varius positions are available to be studied and analyzed (e.g. brain death and organ donation). There are some notable exceptions (i.e. Divrei Chaim on machine matzos), but for the most part the system worked as I've described.
Nowadays, though, we seem to have evolved into a system where pronouncements are made without the need for this "pilpul chaverim" to take place. Sources are not required and general assertions that "the gedolim feel", "all leading poskim hold", and the like are made instead. One example would be the acceptance of Rav Falk's tznius book "Oz V'ahadar Levusha" as a standard text by many in the black-hat community. This despite the fact that many of Rav Falk's opinions are not sourced (or are not supported by his sources) and are hashkafically-based rather than halachikly-based.
Note, my intent is not to attack either Rav Belsky or Rav Falk, who are both tremendous talmidei chachamim; just to note that in the cases I've mentioned, they seem to be ruling without explicating their sources (if they exist). This effectively prevents a "pilpul chaverim", an intellectual approach to discussing these matters and understanding the issues involved.
I would love to see a teshuva that addressed the issue of listening to acapella music during Sefirah and the Three Weeks. I think it'd be a fascinating read. I believe that little work has been done in the area of applying halachik precedents to issues involving music technology. And, I think that interesting arguments can be made on both sides of the issue. Unfortunately, the teshuva I linked in my earlier post missed this opportunity.