[blackcat] L3 Ehlers Spectrogram Indicator

Level: 3


John F. Ehlers introuced Dominant Cycle and Spectrogram Indicator in Mar, 2008.


In "Measuring Cycle Periods" in Mar, 2008, John Ehlers presented a very interesting technique of measuring dominant market cycle periods by means of multiple bandpass filtering. By utilizing an approach similar to audio equalizers, the signal (here, the price series) is fed into a set of simple second-order infinite impulse response bandpass filters. Filters are tuned to 8,9,10,...,50 periods. The filter with the highest output represents the dominant cycle. This script implements a high-pass filter and a six-tap low-pass Fir filter on input, then 42 parallel Iir band-pass filters. Finally, it plots the Ehlers spectrogram as a heat map.

Ehlers Spectrogram indicates market power status:
With high market power, the spectrogram become fuzzy;
With low market power, the spectrogram become distinct.

It also discloses market dominant cycles and subcycles, which indicates the major rhythm. Regarding the rhythm of the market, Chinese and Western cultures have reached a consensus: Dr . Ehlers can find the main harmonic components of the market through DSP analysis via spectrum; Master Zen compares the market rhythm to Bach’s fugue from a philosophical perspective, where there is a rhythm of life.

Finally, please allow me to quote Master Zen’s statement on market rhythm:

"The market is cruel. For those who try to violate the market rhythm, the market is their death place; the market is beautiful, and the market is Bach’s fugue. There is a rhythm of life. Rhythm is always the rhythm of the market. A market participant without a sense of rhythm is always torturing. Put aside your greed and fear and listen to the rhythm of the market. In the weekend, let go of everything, but listen to the rhythm of nature, the rhythm of life, the rhythm of music, and then come back to listen to the rhythm of the market. Dancing with the market, your greed and fear are peeled off one by one, you will become very bright ."

Key Signal

DomCyc--> Ehlers Dominant Cycle
Plot2~Plot60--> Ehlers Spectrum Heat Map

Pros and Cons

100% John F. Ehlers definition translation, even variable names are the same. This help readers who would like to use pine to read his book.


The 73th script for Blackcat1402 John F. Ehlers Week publication.


In real life, I am a prolific inventor. I have successfully applied for more than 60 international and regional patents in the past 12 years. But in the past two years or so, I have tried to transfer my creativity to the development of trading strategies. Tradingview is the ideal platform for me. I am selecting and contributing some of the hundreds of scripts to publish in Tradingview community. Welcome everyone to interact with me to discuss these interesting pine scripts.

The scripts posted are categorized into 5 levels according to my efforts or manhours put into these works.

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Level 4 : script snippets or functions that do not disclose source code. Interesting element that can reveal market laws and work as raw material for indicators and strategies. If you find Level 1~2 scripts are helpful, Level 4 is a private version that took me far more efforts to develop.

Level 5 : indicator/strategy that do not disclose source code. private version of Level 3 script with my accumulated script processing skills or a large number of custom functions. I had a private function library built in past two years. Level 5 scripts use many of them to achieve private trading strategy.

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