[InitialLastName]

In situations where you don't need the archival to be at "perfect reproduction" quality (including things like broadcast archives or recordings of voice comms) you can get by with a 12kHz maximum frequency without losing the essentials (especially clarity of voices). Many adults can't hear much past 12kHz anyway and most music and voice content doesn't have content past 10khz. You don't lose much, but you save half your file size by x2 downsampling.

[Sesse__]

I'd guess the “why” was “why on earth did they not have an antialiasing filter”, not “why did they downsample”. A good lowpass filter is easy to design, cheap to apply, and protects you from this kind of stuff.

[InitialLastName]

I was working off the quote, but I can see some reasons that someone would decide not to AA filter. Depending on the context it might be reasonable to assume that the signal is band-limited anyway (talk-oriented radio especially is often low-pass filtered) and it's easy to miss that some point in the system can introduce an (inaudible to most humans) artifact. Those assumptions, along with the desire to avoid complexity (every step in the signal path is an opportunity for failure) could easily tip you to "just downsample".

I'd also emphasize how little most of the people involved in these systems care about the quality of the archive. If it's good enough to a) confirm there was signal on the channel and b) understand the voices involved, it's good enough to not worry about further.

[kimburgess]

> I'd also emphasize how little most of the people involved in these systems care about the quality of the archive. If it's good enough to a) confirm there was signal on the channel and b) understand the voices involved, it's good enough to not worry about further.

This is uncomfortably accurate. I work with the capture side of these system and people in that space care deeply about the integrity of the signal, but have little concern for what it contains. Archival is the inverse: the information content of the signal is what's important, not the signal itself.