A particular kind of price envelope is "Bollinger Bands" indicator. Upper and lower price range levels are determined by price envelopes. By default, Bollinger Bands are plotted in Tradingview as envelopes at a standard deviation level above and below the price's simple moving average (SMA). I attempted to modify the indicator in this version by adding several kinds of moving averages first. The key feature is that standard deviation should be modified. in Tradingview, SMA calculates the standard deviation. The allocated moving average should be used to calculate the std function when the base line is changed.
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.