See you all in september!
While reading on compact cassette readers (as part of a preliminary study on digitizing archives) I found out that azimuth, or the angle made between the tape and the reading is a considered a big issue, the best case being an azimuth of exactly 90°. I could not, however, quite find what was the effect of varying that angle, even if pretty much everyone agrees that it somehow lessen the tape’s high frequency response. Let’s see how, exactly.
Looking for something else in old notebooks, I found a diagram with no other indication, but clearly a low-cost random generator.
So, why not test it?
Almost ten years ago I wrote an entry about the “1 bit = 6 dB” rule of thumb. This rule states that for each bit you add to a signal, you add 6 dB of signal to noise ratio.
The first derivation I gave then was focused on the noise, where the noise maximal amplitude was proportional to the amplitude represented by the last bit of the (encoded) signal. Let’s now derive it from the most significant bit of the signal to its least significant.
The idea of reorganizing data before compression isn’t new. Almost twenty five years ago, Burrows and Wheeler proposed a block sorting transform to reorder data to help compression. The idea here is to try to create repetitions that can be exploited by a second compression engine.
But the Burrows-Wheeler transform isn’t the only possible one. There are a few other techniques to generate (reversible) permutations of the input.