Blog Profile / The Endeavour


URL :http://www.johndcook.com/blog/
Filed Under:Academics
Posts on Regator:1289
Posts / Week:4.9
Archived Since:April 26, 2011

Blog Post Archive

Kalman filters and bottom-up learning

Kalman filtering is a mixture of differential equations and statistics. Kalman filters are commonly used in tracking applications, such as tracking the location of a space probe or tracking the amount of charge left in a cell phone battery. Kalman filters provide a way to synthesize theoretical predictions and actual measurements, accounting for error in […]

Cepstral alanysis vocabulary

An earlier post defined cepstrum and quefrency. This post explains some of the other quirky terms introduced in the same paper by Bogert, Healy, and Tukey. (Given Tukey’s delight in coining words, we can assume he was the member of the trio responsible for the new terms.) The paper [1] explains why the new twists on […]

Selecting clients

One of the themes in David Ogilvy’s memoir Confessions of an Advertising Man is the importance of selecting good clients. For example, he advises “never take associations as clients” because they have “too many masters, too many objectives, too little money.” He also recommends not taking on clients that are so large that you would lose your independence […]

How about one good one?

I’m no fan of tobacco companies or their advertising tactics, but I liked the following story. When the head of a mammoth [advertising] agency solicited the Camel Cigarette account, he promised to assign thirty copywriters to it, but the canny head of R. J. Reynolds replied, “How about one good one?” Then he gave his account to […]

Cepstrum, quefrency, and pitch

John Tukey coined many terms that have passed into common use, such as bit (a shortening of binary digit) and software. Other terms he coined are well known within their niche: boxplot, ANOVA, rootogram, etc. Some of his terms, such as jackknife and vacuum cleaner, were not new words per se but common words he […]

Bring out your equations!

Nice discussion from Fundamentals of Kalman Filtering: A Practical Approach by Paul Zarchan and Howard Musoff: Often the hardest part in Kalman filtering is the subject that no one talks about—setting up the problem. This is analogous to the quote from the recent engineering graduate who, upon arriving in industry, enthusiastically says, “Here I am, […]

Top tweets

I had a couple tweets this week that were fairly popular. The first was a pun on the musical Hamilton and the Hamiltonian from physics. The former is about Alexander Hamilton (1755–1804) and the latter is named after William Rowan Hamilton (1805–1865). Hamiltonian: The new Broadway hit about the sum of potential and kinetic energy. pic.twitter.com/PCJk3imDsq […]

Tonal prominence in a leaf blower

This afternoon I was working on a project involving tonal prominence. I stepped away from the computer to think and was interrupted by the sound of a leaf blower. I was annoyed for a second, then I thought “Hey, a leaf blower!” and went out to record it. A leaf blower is a great example of […]

Loudness and sharpness

This post looks at loudness and sharpness, two important psychoacoustic metrics. Because they have to do with human perception, these factors are by definition subjective. And yet they’re not entirely subjective. People tend to agree on when, for example, one sound is twice as loud as another, or when one sound is sharper than another. Loudness Loudness […]

Electric guitar distortion

The other day I asked on Google+ if someone could make an audio clip for me and Dave Jacoby graciously volunteered. I wanted a simple chord on an electric guitar played with varying levels of distortion. Dave describes the process of making the recording as Fender Telecaster -> EHX LPB clean boost -> Washburn Soloist […]

Demystifying artificial intelligence

Computers do what we tell them to do. Period. Any talk of computers doing things they weren’t programmed to do is only a way of speaking. It’s a convenient shorthand when used properly, misleading mysticism when used improperly. When you write a program print(247) you could say that the computer isn’t programmed to print the number […]

Optimistic about humans in aggregate

Russ Roberts from his most recent podcast: I’m a very optimistic person, and I have a lot of faith in the human enterprise writ large—not so much in any one human. I have very little faith in any one human, which is why I’m suspicious of experts and power that is centralized.

Converting between Hz, Barks, and music notation

I’ve written before about how to convert between frequency and pitch and scientific pitch notation. I’ve also written about the Bark scale. Here’s a little online calculator to convert between Hz, Bark, and music notation. You can enter one of the three and it will compute the other two.  

Spectral flatness

White noise has a flat power spectrum. So a reasonable way to measure how close a sound is to being pure noise is to measure how flat its spectrum is. Spectral flatness is defined as the ratio of the geometric mean to the arithmetic mean of a power spectrum. The arithmetic mean of a sequence […]

Family tree numbering

When you draw a tree of your ancestors, things quickly get out of hand. There are twice as many nodes each time you go back a generation, and so the size of paper you need grows exponentially. Things also get messy because typically you know much more about some lines than others. If you know […]

The acoustics of kettledrums

Kettledrums (a.k.a. tympani) produce a definite pitch, but in theory they should not. At least the simplest mathematical model of a kettledrum would not have a definite pitch. Of course there are more accurate theories that align with reality. Unlike many things that work in theory but not in practice, kettledrums work in practice but not in theory. […]

How to create Green noise in Python

This is a follow-on to my previous post on green noise. Here we create green noise with Python by passing white noise through a Butterworth filter. Green noise is in the middle of the audible spectrum (on the Bark scale), just where our hearing is most sensitive, analogous to the green light, the frequency where […]

Green noise and Barks

Colors of noise In a previous post I explained the rationale behind using names of colors to refer to different kinds of noise. The basis is an analogy between the spectra of sounds and the spectra of light. Red noise is biased toward the low end of the audio spectrum just as red light is […]

Consecutive pair magic square

The following magic square has a couple unusual properties. For one, numbers appear in consecutive pairs. Also, you can connect the numbers 1 through 32 in a continuous path. I found this in Before Sudoku. The authors attribute it to William Mannke, “A Magic Square.” Journal of Recreational Mathematics. 1 (3) page 139, July 1968. […]

How to digitize a graph

Suppose you have a graph of a function, but you don’t have an equation for it or the data that produced it. How can you reconstruction the function? There are a lot of software packages to digitize images. For example, Web Plot Digitizer is one you can use online. Once you have digitized the graph […]

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