Michael Lee Posted August 24, 2021 Share Posted August 24, 2021 The tone vocoder was one of the earliest methods developed to transmit voice digitally through low-bandwidth networks. In the original tone vocoder method, an input voice was transformed into time-frequency space, where at each time interval the sound was decomposed into a series of frequency bands. The amplitudes of the bands were transmitted over wire or radio. On the receiver side, the amplitudes were used to reconstitute the original audio. The quality of the tone vocoder was never that good, and modern methods such as linear predictive coding (LPC) have superseded it. However, for spirit transmission, the simplicity of the tone vocoder is useful. In modern times, the term "vocoder" is used either to 1) describe methods for using vocals to modulate instruments in music using the aforementioned tone bank approach, or 2) converting audio to a time-frequency space to perform operations such as changes in pitch and speed (aka, a phase vocoder). Why would a tone vocoder be good for spirit communication? One hypothesis is that spirit is only able to add short impulses of energy into our devices. No matter how hard they try, a bunch of pulses strung together doesn't sound very voice-like. What if their impulses could be interpreted as musical notes that play as short duration tones? We set up a communication system with spirit where in a given 16,384 sample block (1.024 seconds at a 16 kHz sampling rate), there are 32 time intervals and up to 64 tones that can be activated in each of these intervals. The tone detection of the spirit signal we (spirit and physical experimenters) agree upon is a pulse-position-modulation (PPM) approach. Within a 32 ms time interval, there are 64 sub-intervals. If the amplitude / energy of the signal (or the inverse amplitude for null detection) within a sub-interval is above a threshold (peak detection), the respective tone is activated during that interval. We found it useful to increase the duration of each activated tone by 2-3x ( to about 60 ms, which is the typical duration of a medium-length vocal phoneme). The frequencies of interest for synthesis of human speech are between 75 Hz and 4kHz. Therefore, the agreed 64 tones can be linearly spaced within this range. One can also choose a non-linear spacing (like quadratic or exponential/musical). For the linear spacing, the 64 tones can range say from 168 Hz up to 4200 Hz, with equal spacing of 64 Hz. My spirit team has learned how to activate this vocoder to produce voice. I suspect that any future researchers will have similar success with heaven-level spirit teams. Spirits use the term "mirror" to describe the device that converts their voice to tone index conversion (likely a Fourier transform). They use the term "elevator" to describe the fact that over a 32 ms interval, hitting at the right moment activates a particular tone, starting from low frequency (168 Hz) to high (4.2 kHz). They also use the term "modem," because, indeed, this is a digital-like transmission protocol. I should point out here, too, that, in theory, my configuration is not too different than when researchers use a sweeping frequency. With a sweep, the spirits can "push" the sound at certain times corresponding to different frequencies. Of course, effects like noise gating (to hide original tone) and reverb (to extend the "escaped" tone) are needed. If spirits could perfectly activate tones in this system to produce voice, it might actually sound fairly legible. However, even perfect musical speech isn't all that easy to understand. Therefore, I've developed machine learning models to convert the musical speech to real-sounding speech. The way I do this is I convert real speech phrases into tones, and then train an ML model to reverse those tones back to the original speech. In my next post, I will share some results... 1 Quote Link to comment Share on other sites More sharing options...
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