More crackpot thinking from Glenn Greenwald

[struggle4progress]

82. One shouldn't confuse the radio channel signal with the conversation. When cell phone companies

sample a conversation for digital conversion, with the aim of increasing the number of conversations carried at a certain frequency, their aim is to chop the conversation into packets that can be interspersed with packets from other conversations, so the signal along the radio channel typically consists of interspersed packets from a number of conversations, and this signal itself generally has no law enforcement or intelligence interest

What might have actual law enforcement or intelligence value is a particular reconstructed conversation, and the federal statutes, that require telecom companies to be able to comply with multiple wiretap court orders, actually require the companies to be able to deliver the conversations themselves from the channel stream

For law enforcement purposes, it will be much more satisfactory to have the telecom itself reconstruct the conversation, with the existing network technology actually used for the communication, than to have the telecom provide to a government agency the compressed version of the conversation and to have the government then reconstruct the signal, because off-site third-party reconstruction is subject to defense objections that reconstruction errors have introduced additional misleading audio distortions

The same sort of objection applies to governmental recompression of reconstructed audio for storage purposes. If (for example) the original conversation was sampled at a certain rate to produce numerical data for compression based on fourier analysis, the sampling rate limits the frequency modes that can be accurately reproduced, and higher frequency modes are not accurately captured by rather appear as aliasing errors in the reconstruction. If the original reconstruction is subsequently compressed and decompressed by an algorithm differing from the original algorithm, it is therefore possible under some circumstances to introduce additional deviations from the original

So agencies obtaining cell phone conversations under court order are likely to want the provider's highest-possible quality reconstruction of the conversation from the signal, rather than the radio channel data, and (so far as is feasible) they are unlikely to further compress and decompress the reconstruction delivered to them by the provider