There are a lot of bands type indicators and almost all are working in a very similar way: some basic value is taken to be a central value and the bands are drawn on equal distances up and down. That encloses the prices very well, but usually causes a lag when there is a trend reversal (since the opposite side band is too far from the current price).
This indicator is one of the ways to avoid that. Instead of using equidistant bands, the bands are asymmetric.
When the price is above the average, then the lower band is narrowed. Also, when the price is bellow the average the upper band is narrowed. That makes the "opposite side" band much closer after some time to the average and it makes the signals on bands breaking faster and sooner than any "regular" bands indicator.
This version of Synthetic RSI is using Ehlers smoothed RSI in calculation instead of using "regular" RSI and that makes the resulting synthetic RSI even smoother.Synthetic RSI
Instead of using one RSI, the Synthetic RSI indicator is using 3 instances of RSI. Those 3 instances of RSI are then used to calculate the "synthetic" value (that is not an average of the 3 since the calculation differs from an average).
MACD High/Low uses the highest high and lowest low of MACD (nnn) bars back to calculate a sort of dynamically changed zero line, early levels up and down and trend confirmation levels up and down. By adding these non-fixed levels, the MACD becomes faster in response to market changes and the MACD trend assessment has less false signals.Nonlinear regression
This indicator is a MetaTrader 5 version of nonlinear regression. Nonlinear regression is very "fast" when responding to sudden market changes so the default calculation period is set to somewhat longer period than it is usual for similar type indicator. Because of that some experimenting with period is advised based on your trading strategy and trading style.