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▷ How could astronauts have communicated so clearly and noiselessly with ground control, when the noise level of the propulsion engine, a few feet away, directly below them, was reported to have been totally deafening?

Appropriate microphone design on the transmitting end, and a squelch circuit on the receiving end, i.e.:

•   microphone designed to have a pattern of sensitivity that sensed sound only from the direction of a helmeted astronaut's mouth, and for a range that extended not much deeper into the helmet.  The sensitivity pattern is typically described by the mathematical name of a shape that's defined by a trigonometric formula.  A dynamic-type microphone, which was in the radio-enthusiast market no later than the mid-1960s, would've helped the voice-quality.  Reducing the microphone's sensitivity to sounds outside the helmets would've muffled the sound of the engines that was deafening to humans riding the rocket stages.  Getting those characteristics in a device sufficiently miniaturized for a spacesuit might've been the primary engineering challenge.

•   squelch is a receiver feature that provides control of the volume-threshhold of received sound that's produced as output (i.e., via headphones or speakers).  It eliminates all sounds with a lower volume than that for which it's set, but passes thro' all sounds of higher volume at their original volume.  It's conventionally controlled in radio receivers by a ‘volume’-like rotating knob, and used on Earth to eliminate the distraction of noise caused by various kinds of radio interference.

The combination of an appropriate microphone designed to have insensitivity  that would've muffled the deafening sound of the engines, and squelch that could then eliminate the muffled sound, would've produced the sounds of clear and noiseless voices that listeners are accustomed to hearing during U.S. spaceflights.

By the way, most of the abruptness of sounds heard is because it's radio--not telephone--communication technology, so voice-actuated switching (VOX) is an important part of the system.  VOX circuits mediate all the voices potentially contending for radio transmitter channels, notably  the numerous voices at Mission Control.

Below is a 55 second portion of a video link I published earlier.  I am trying to spare folks like 5micro, (and maybe [Alli]gatordic[a]x) the tedium of watching anything longer than that.  From a previous remark, I conclude that 5Micro doesn’t care for videos, so I purposely publish again only this excerpt. [....] The video excerpt was made, I believe in 2015.

Yes, by all means, please include me among "doesn’t care for videos": AlligatorDicax.  Debating by shovelling videos without citations into topics is at best a habit of laziness.

I assume that [Col. Virts] speaks on behalf of the entire space industry.  If not, please enlighten me further.

Really?  I would not assume that.  I  assume only that he speaks only for himself, with any "we" being a use of that pronoun that very informally refers to his past-fellow astronauts, or more broadly, the citizenry of the U.S.A.  Established manufacturing companies or their industry-benevolent organizations (e.g., aerospace), federal agencies (e.g., NASA), and military services, can get really upset if people claim to speak for them when such people have not been explicitly authorized to do so.  It can be "career limiting" if its severity isn't deemed a firing offense.

[....] if Virts is not an actor or an impostor, and reflects the cold, bare facts presently, then some further explanation is in order.  Since we live in time, consisting of past, present and future, events must line up accordingly.  If in 1969, at the launch of the first (successful) Apollo moon landing mission, the technology did not exist for sending a manned space vehicle beyond earth’s orbit, how can we be celebrating in 2019 events which could not have yet possibly taken place, in light of Virts’ unambiguous remarks in 2015?

[<]https://www.youtube.com/watch?v=JgXDi7mc43M]https://www.youtube.com/watch?v=JgXDi7mc43M[>]

How could "we" be "celebrating in 2019"?  Simple: Your premise that "the technology did not exist" in 1969 is false.

If Virts' remarks are as unambiguous as you claim, we wouldn't need to worry about subtleties, like tone-of-voice.  So why wouldn't you spare CathInfo readers the cuмulative time-sink of watching yet another video shovelled into a topic, and instead provide us with exact quotes--maybe even a full unedited transcript--hmmm?  It's you who claimed that it sinks only 55 seconds of each reader's life--or better yet: only yours!

In [the video cited by hollingsworth,] Virts, in clear, unmistakable language, states that “we” do not have space travel technology capable of launching “us” beyond earth’s lower orbit.

That should be phrased as "lower-Earth orbit"[*].

But!

He said "right now we can only fly in earth orbit" - the US today doesn't have the operational technology to go to the moon.  He did not say the US never did.

Well, great leapin' L.E.M.s!  That looks for all the world like an exact quote, followed by a valid conclusion!

A moon trip requires a human-rated heavy-lift launch system with enough delta V to get to the moon.  The only US operational, human-rated heavy-lift launch system was Saturn V.  They were used.

That's "used" as in "launched" or "flown".

A total of 15 flight-capable vehicles were built, but only 13 were flown.

The unflown 2 vehicles (of the 15) were either honored by being put on display, or ingloriously scrapped, after Apollos 18--20 were cancelled by some combination of the Johnson (1963--1969) and Nixon (1969--1974) Administrations.  Lyndon's Great Society, plus the on-going Vietnam War (as escalated or widened by both) were expensive, doncha know?

So were all the N1 (the Russian counterpart to the Saturn V).

Welll, yesss, "used" in a manner of speaking: The N1 never became operational, because all 4 N1 test launches failed (Feb. 1969--Nov. 1972).  Just 2 weeks before Apollo 11, what was reckoned as the 2nd N1 test-launch resulted in a spectacularly powerful explosion that destroyed its launch facility.  Even tho' 'twas a project of the Godless Communist Russians, advocates of space-exploration should be excused if they express some sympathy for all the setbacks, many being political or interpersonal, that were endured by the engineers & scientists in their manned lunar project.  Reportedly, N1 was suspended in 1974, after Project Apollo had already concluded, and later, N1 was cancelled in 1976 [×].  It's a mystery to me why the Kremlin would've waited so long to pull the plug on a project that would earn them no better than the 1st runner-up trophy.  I don't know how soon Brezhnev (1964--1982) began to advance his newfangled ambition of launching a Soviet blue-water (i.e., open-ocean) Navy, but that would require spending lots of rubles from the Soviet budget.

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Note *: All astronomical or creationist -centrism debates have prudently been banished by Matthew to the CathInfo sub(sub)forum <https://www.cathinfo.com/the-earth-god-made-flat-earth-geocentrism/>.

Note ×: <https://en.wikipedia.org/wiki/N1_%28rocket%29>.  It's written in an authoritative style, but it's distressingly deficient in cited sources, almost as if some N1 enthusiast(s) Godlessly plagiarized a single source, e.g., a book chapter from a book published in the West by 1 of Khruschev's children (i.e., at least 1 son and 1 daughter).  Of course, no exposés of the Soviet Space Program, being among R&D programs for the Strategic Rocket Forces, would've leaked out of the Kremlin or Kazakh S.S.R. before Glasnost and "The Fall of the Soviet Union".