Range Filter

A recursive deadband filter that only moves when price closes further than its own smoothed typical range.

What it is

The Range Filter is a trend-smoothing overlay popularized by a widely copied open-source TradingView script, usually attributed to the user DonovanWall. Despite enormous usage it has essentially no formal documentation, so this page reconstructs the mechanics directly from the published code. The core idea is a deadband filter: the indicator measures how far price typically moves from bar to bar, smooths that measurement, and then draws a line that only moves when the close travels further than that typical amount. Small moves are absorbed — the line stays flat — while larger moves drag it up or down, with bands plotted one smoothed range above and below the line. The result looks like a step-line that is colored one way while rising and another while falling, and most versions print arrows when the direction changes. It is a noise filter, not a forecast: it re-describes past closes with sub-threshold movement removed, and it carries no information about future price. This is educational content only, not financial advice; no indicator predicts price, and trading involves risk of loss.

How it works

The calculation has three stages. First, measure movement: take the absolute one-bar change in close, |close − close[1]|. Second, smooth it twice: an EMA of that absolute change over the sample period (default 100), then an EMA of the result over (2 × period − 1) bars, multiplied by the range multiplier (default 3). This 'smoothed range' is the deadband half-width. Third, update the filter recursively: if the close is above the previous filter value, the new value is the maximum of the old value and (close − smoothed range); if the close is at or below it, the new value is the minimum of the old value and (close + smoothed range). In plain terms, the line refuses to move unless price closes more than one smoothed range beyond it, and it never moves against the side price is on. Direction is simply whether the filter rose or fell versus the previous bar, and the popular scripts color the line and print arrows on direction changes. Because the filter is recursive, each value depends on the entire prior series, so two charts with different history lengths can disagree slightly near the start of the data. On confirmed bars the calculation is deterministic and does not repaint.

How traders read it

• The line's slope and color describe the current filtered direction; a flat line means price has stayed inside its own smoothed noise band.
• The bands at filter ± smoothed range show exactly how far the close must travel to move the line — they are the deadband edges, not support or resistance.
• Direction flips are lagging by definition: the line turns only after price has already traveled a full smoothed range past it.
• A larger multiplier gives a flatter line with fewer, later flips; a smaller one tracks price closely and flips constantly. Neither setting is 'correct'.
• The arrows in popular versions mark the line's direction change — the same information as the color, not additional confirmation.
• Clones differ: some smooth high/low ranges or change the EMA lengths, so two 'Range Filter' scripts can print different signals on the same chart.

Common settings

The viral script's defaults are a sample period of 100 and a range multiplier of 3, applied to the close. Both numbers are conventions from the original code, not derived values. Shorter periods make the smoothed range react faster to volatility changes; larger multipliers widen the deadband. Because flip counts change dramatically with small parameter changes, it is worth mapping behavior across a grid of settings on your own data before relying on any single pair.

Strengths

• Makes the noise threshold explicit and tunable, instead of hiding it inside a fixed-length average.
• Flat-line behavior visually separates ranging stretches from directional ones without a second indicator.
• Deterministic and non-repainting on confirmed bars — every value can be recomputed and audited.
• The recursion is only a few lines of arithmetic, so it is easy to verify a port against the original once the formula is written down.

Pitfalls to watch

• Extreme settings sensitivity: the 100/3 defaults are arbitrary, and modest changes to either number can multiply or eliminate flips on the same chart.
• Whipsaw: with a small multiplier or in choppy markets the line flips repeatedly, each flip arriving after the move that caused it.
• Lag by design: the filter cannot move until price has already closed a full smoothed range beyond it, so entries based on flips are always late to the move.
• Undocumented variants: many clones alter the smoothing or band logic while keeping the name, so signals are not comparable across scripts without reading the code.
• Recursive start-up dependence: values near the beginning of available history differ from those computed on longer histories, which can quietly change early backtest bars.
• No predictive power: the filter re-describes past closes with noise removed. It does not forecast price, and no indicator removes the risk of loss.

Pine v6 example

//@version=6
indicator("Range Filter Example", overlay = true)

per = input.int(100, "Sample Period", minval = 2)
mult = input.float(3.0, "Range Multiplier", minval = 0.1, step = 0.1)

absChange = math.abs(nz(ta.change(close)))
avgRange = ta.ema(absChange, per)
smoothRange = ta.ema(avgRange, per * 2 - 1) * mult

var float filt = close
filt := close > filt ? math.max(filt, close - smoothRange) : math.min(filt, close + smoothRange)

isUp = filt > filt[1]
isDown = filt < filt[1]

plot(filt, "Range Filter", color = isUp ? color.teal : isDown ? color.red : color.gray, linewidth = 2)
plot(filt + smoothRange, "Upper Band", color = color.new(color.gray, 70))
plot(filt - smoothRange, "Lower Band", color = color.new(color.gray, 70))

flipUp = isUp and not isUp[1] and barstate.isconfirmed
flipDn = isDown and not isDown[1] and barstate.isconfirmed
plotshape(flipUp, "Turn Up", style = shape.triangleup, location = location.belowbar, color = color.teal)
plotshape(flipDn, "Turn Down", style = shape.triangledown, location = location.abovebar, color = color.red)

Pro tip: Before using any Range Filter setting, count its direction flips across a range of period/multiplier pairs on your instrument — if the flip count swings wildly between neighboring settings, the signals you see are largely a parameter artifact rather than a property of the market. Gate alerts on bar confirmation so live behavior matches closed-bar behavior. Educational information only, not financial advice; no indicator is predictive, and trading involves risk of loss.

Educational only — not financial advice, not a recommendation to trade. No indicator is predictive; trading involves substantial risk of loss.