Ear Tips for Noise Canceling Headphones

Most people have never tried in-ear headphones. They get ear wax on them, so to don’t share well. Wearing them on stage, musicians can hear their own instruments without going deaf. Since musicians use them for performance in-ear headphones are also called monitors, just like the speakers that point toward the band from the front of the stage.

Distraction, from airplane noise, office noise, maybe your own keyboard, annoys. Three headphones solve the problem. Most famously, Bose’s active noise canceling Quiet Comfort line and similar products by other makers. Passive noise reduction from sealed over-ear headphones is about 10 dB. In-ear monitors offer passive isolation between 20 and 30 dB.

I demoed the Bose phones years ago, and they hissed with the noise cancellation on. The sound quality was neither exceptional nor awful, but was poor for a $300 price. World-class sound quality is available from makers like Etymotic and Westone with in-ear monitors that provide as much isolation as active noise canceling models.

But in-ear monitors have one major drawback, they go in your ear canal. That means that they can get gross with ear wax, can be painful or itchy, and they can wear out. In my nine years using in-ear monitors I only ever found the foam tips from the manufacturer comfortable. The three-flange silicon tips isolate amazingly, but itch like fire after twenty minutes and hurt like a drill after sixty. The foam tips are comfortable, almost as isolating as the three-flange tips, but cannot be fully cleaned and wear out after three months.

tip_catalog

The most recent time I wore out a pair of foam tips, I decided it was time to look at the alternatives. I hoped to find, ideally, a comfortable silicon tip with the isolation of the foam tips or an inexpensively replaceable foam tip. It seems to be sort of a niche market, and I failed to find any useful comparisons on the web. So, I did my own.

I purchased a sizing kit from Westone, another from Monster, and a pack of the universally-liked Comply foam tips. Testing included a few leftover tips from the headphone’s original purchase, and I included those in the comparison.

I evaluated each tip for fit, seal, pain, itching, sound quality, isolation, and microphonics. Fit, seal, sound quality, and isolation are all related. With in-ear phones a poor seal means poor isolation and poor bass response and poor sound quality. Good fit depends on having the correct size tip for your ear. Medium tips from most manufacturers fit my ears well. The calipers in the picture below show a base diameter around 0.465 in (1.18 cm).

comply-tip-size

Most of the tip designs are old. Grubby among my grandfather’s shooting supplies, foam and triple flange tips were familiar to me twenty-five years ago. Recently Westone introduced a single-flange tip focusing on good seal and comfort. These, along with other single-flange tips, suffer from awful microphonics. When cables rub against anything, like your arm as you move the mouse, the motion travels along the cables and makes loud popping noises. Single-flange tips have the worst microphonics.

The best overall tips for me are Comply’s T-100 PLT medium foam tip. They cause no pain or itching, seal great and offer very good isolation, have low microphonics, and sound very good. Like all foam tips, they will wear out in three months and get waxy and gross. And they are neither the most isolating nor the quietest.

The best sounding tips are the Westone silicone three-flange tips, which offer by far the best isolation and by a small margin the best sound. After twenty minutes they also offer crushing pain and infernal itching. The three-flange tips have a place in my kit, but I don’t use them long.

Westone’s single flange tips are silicone, and are comfortable. My notes describe the itching from Westone’s silicone three-flange tip as extreme. After that, finding any silicone tip bearable was a surprise. The Westone Star tip is comfortable. It has poor microphonics, and poor isolation; it has no place on an airplane or a noisy office. On the other hand, Star Tips are cleanable and provide some isolation, so they are candidates for the gym. These also have a place in my kit.

The rest of the tips are unsurprising. Everything from Monster had poor isolation and had distracting microphonics due to a poor design. All of the other fitting foam tips are acceptable, but none are as good as Comply’s. All the other silicone tips are unacceptable for me, too painful, too itchy, too microphonic, and sound too poor. The results for all tips that fit reasonably well are in the table at the end.

I tested these tips with an hour-long playlist from mixed genre, seven songs in all. It starts with D. Barenboim/Berliner Staatskapelle recording of Beethoven’s Symphony 9, included to show dynamic range of symphonic instrumentation. The next two songs have typical mid-pitch-heavy pop songs including Adele’s One and Only off her album 21, and Erica Badu’s Four Leaf Clover from Baduism. Next, Erica Badu’s Rimshot shows the performance with an extreme deep bass opening line. Sweet Jane from the Cowboy Junkies is more typical pop. A mid-heavy but delicate sound and detailed sound from Miloš Karadaglić’s album Mediterráneo with his performance of Granados’ Danzas españolas, Op.-No. 2 Oriental. Finally, a very detailed song from Rush, The Necromancer off their album Caress of Steel has shown the weaknesses of many sound systems. I chose an hour-long playlist because in my experience in-ear monitors often lead to such itching and pain in the ears that I want to claw them out of ears screaming after forty minutes.

Monster produced the only foam tips I avoid. To fit my earphones you put the tiny red rubber rings around the earphone and then slide the tip over the top. The result was poor isolation and poor microphonics.

monster-tip

Tip

Size

Fit

Seal

Sound

Iso.

Mic.

Pain

Itch

Westone Classic Foam

Med

G

G

G

G

G

G

G

Westone Silicone White 3-flange

G

E

E

E

G

M

VP

Comply Foam T-100 PLT

Med

G

G

VG

VG

VG

VG

VG

Westone Star Silicone Black 1-flange

Med

G

G

VG

P

P

VG

VG

Westone Classic Foam

Med-Long

G

G

G

G

G

VG

G

Westone Truefit+ Foam

Med

G

G

G

G

G

G

VG

Westone Silicone Black 1-flange

Med

G

G

G

G

P

G

G

Westone Star Silicon Black 1-flange

Med-Long

G

G

VG

P

P

P

G

Weston Truefit+ Foam

Med-Long

G

VG

G

VG

G

G

G

Westone Silicone Clear 1-flange

Med

G

P

P

P

P

P

G

Westone Classic Foam

Small-Long

G

P

P

P

G

VG

G

Monster Foam

Med

G

G

G

P

P

G

G

My wife put me onto Bloglovin for those who follow with an aggregator. If you like, Follow my blog with Bloglovin. Finally, I have had no contact with the makers of these products, and I wasn’t compensated or paid in any way. Quite the contrary, I bought all the equipment reviewed here.

Some Curious Micrographs

We have an old microscope and a camera adapter for it. Occasionally we dig it out, and light some small stuff up. Several weeks ago my son’s science workbook had a multiple choice question, roughly “which of these would look different under a microscope”

  • salt in water
  • sugar in water
  • pollen in water

An experiment seemed in order. After exploring those boring solutions we explored other things. The first is the tip of a technical pen. I believe the narrow diameter part is the wire, and the large diameter is the tube. I suppose the fillet is a meniscus of ink.

Rotring Technical Pen Tip

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The feather is cool enough to look at, but within the feather is a single fiber from a blue yarn that my wife was crocheting with.

A Feather and a Colored Thread

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At the request of my son, I plucked one of my precious head hairs. I had hoped to see the surface structure of the hair, a tiny scaled surface. It is visible, but not clearly. Still, pretty cool.

A Hair at the Root

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We looked at paper, too. But paper was not that interesting until we compared three different types. Notebook paper, a Kleenex, and slice of technical drawing paper (like vellum). The difference between the fibers is amazing.

A Tissue and a Strip of Technical Drawing Paper

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My son wanted to look at candle wax too, but the toothpick we used to get it is far more interesting.

Toothpick with Candle Wax

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You think that milk has been homogenized and so it should look like a smooth, uniform material. I was fascinated to observe a sandy or granular structure under an optical microscope. The microscope cannot really resolve the individual particles, but it can show that the particles are there.

Milk

20140207-24

The final picture is shows the microchip inside a slow-fade RGB LED. This LED fades through the gamut of colors, and macroscopically looks identical to any other LED. The picture is blurry because it is imaged through the acrylic body of the LED. Nevertheless, the microchip structure is visible. At the bottom you can see four solder joints, one for ground (or Vcc) and red, green, and blue components.

Microchip Inside a Slow-fade LED

20140207-29

Typefaces

Updated February 5, 2014 to correctly display the LaTeX screenshot, minor prose edits, and added discussion of font styles.

I do not know if you have a favorite font. I do. I really like Microsoft’s Calibri font because it is very readable on screen and paper and it looks professional. With that in mind, it has several huge shortcomings for much work. Let me list

  • You don’t have a right to use the font unless you have purchased it (for $120) or acquired with a legal license of a Microsoft product that includes it.
  • Calibri does not have small caps family member
  • Calibri does not have a corresponding math font

Many people, including me, got to know Calibri because it is the default font in Microsoft Word. I am trying to find a way to leave Word because it has poor support for equation numbering, mediocre bibliography support. It is also difficult to automate updated graphics using non-Microsoft work flow. For example, I often generate graphics in Python with Matplotlib and write them to a file. I would like my document workflow to pick up the picture automatically when it changes but have not found a reliable way to do this in Word.

Microsoft Word is fundamentally poor at rendering documents compared to a display tool like Adobe Reader. Consider the following screenshot comparing a default Word document snippet in Calibri with Word’s rendering of text in the TeX Gyre Bonum OpenType font. Next screenshot is from a Word display at 100% zoom.

word_example

The shading in the Bonum section is appalling. Look at the dot over the letter i in pi. Word renders the compatible TeX Gyre Bonum Math and TeX Gyre Bonum fonts differently depending on whether it is in equation mode or body text. The shading in the top paragraph is good; however, the overall construction is horrible. In Word a number in equation mode is displayed in the default math font Cambria. Calibri does not match Cambria and the two numbers can’t look the same. Furthermore, the fraction in the middle of the paragraph causes the line spacing to expand just on that line, making it look almost like there are more paragraph breaks than there should be. Distracting and unattractive.

The next picture is screenshot from Adobe Reader X at 100% zoom viewing a LuaLaTeX generated LaTeX document.latex_example

First, the TeX Gyre Bonum snippet is readable and reasonably good looking. The math font and text font are indistinguishable, as they should be. LaTeX handles even Microsoft’s pet font Calibri better than Microsoft. The fraction renders clearly and readably. It does so without creating a large horizontal gap.

The ideal faces, from my point of view, should:

  • Be embeddable in your electronic documents
  • Not cost much to install on every system you want to use (eleven computers at least)
  • Work on Windows, Linux, and MacOS
  • Include regular, bold, italic, bold italic, small caps, and math families
  • Be functional with Word or other non-LaTeX tools.

The license problem is unquestionably the most limiting factor since OpenType now seems to allow fonts to work across platforms. The GUST project has created a series of libre fonts called the TeX Gyre fonts. Among these fonts, only three have the math family, and all three of these satisfy the other requirements.

TeX Gyre Bonum Based on URW Bookman L
TeX Gyre Pagella Palatino-like
TeX Gyre Termes Times-like

There are several other Gyre fonts that are quite attractive and potentially useful but lack the math fonts. TeX Gyre Schola seems to be planning a math font which is not yet ready. If you don’t need to have a math font, or don’t need a matching math font then there are many other fonts to consider. Fontsquirrel has a lovely list of libre fonts. There are other fonts available for LaTeX that can produce good results but do not seem to have a functional method to work with other tools.

Wikipedia describes Calibri as a “humanist sans-serif typeface”. The closest TeX font with math support, to my eyes, is KP Sans-Serif. The strokes are not as modulated so the KP looks less refined than Calibri. I do not see how to use that typeface outside of LaTeX. If you are interested in other LaTeX fonts, consider looking at the LaTeX font project fonts with math support.

In Youth and Beauty

I bought two pieces of art to hang from my son’s elementary school. I loved them immediately. The abstract tiles where done by my son’s 3rd and 4th grade class. The tree was made by a 1st and 2nd grade class. Both pieces of art are really lovely. The tree has a cool property, like a scene in Ferris Bueller. The art changes its character from far away to as close anyone would care to get. First, the tiles of abstract images of persons and animals was made under the rule that the student not pick up the pen during the drawing and then there are rules for filling with color, like a graph coloring rule.

20131230-05

The other artwork is a sort of mosaic of paper circles colored and glued to a black foam core board. The tree shots zoom in with three steps doubling the zoom at each step.

01-20131224-Tree

 

02-20131224-Tree-inset03-20131224-167

 

04-20131224-167-inset05-20131224-168

 

06-20131224-169-inset07-20131224-171

Arduino Flickering Candle

Update December 24, 2013: Mokus refined his code so that the distribution is now well-behaved (nearly normal) and the PSD no longer turns up at high frequencies). The plots and post have been updated to reflect this change. He will push code to the same link as available.


In my previous post on Candle Flame Flicker I describe the statistics of the optical intensity flicker from a candle in terms of the probability density of the brightness samples and in terms of the power spectral density of the brightness. In this article I discuss how to make an Arduino drive an LED to flicker in a way that is statistically similar to the measurements I took on a real candle.

In the measurements I observed the spectral roll-off of the candle to start between about 5 and 8 Hz, and to decline at a nominal rate of around 44 dB for each decade increase in frequency. The 2nd-order infinite impulse response filter is computationally efficient in terms of using a small amount of memory and requiring few calculations. However, the Arduino is not good at floating point arithmetic. On the Arduino, floating point is done in software, has relatively few bits of precision, and is about 4 to 40 times slower than fixed point (integer) math. It is quite difficult to find useful benchmarks. The basic process is to create white noise and then filter it to the correct spectral shape. Afterward, the signal is scaled to have the appropriate variance and offset with a constant to represent the average brightness of the “flame”.

The approach I used was to design the IIR in Python with scipy’s signal module. I specified a 2nd order lowpass Butterworth filter, specifying a cutoff frequency of 8 Hz, and a sample frequency of 60 Hz. I normalized the coefficients to work in a 16 bit integer space, following Randy Yates’ 2010 Practical Considerations in FIR Fixed Filter Implementations, mainly. From a synthesis perspective, there is some prior art. Philip Ching, a student at Cornell synthesized candle noise quite cleverly, though he neither reported nor replicated the correct statistics. A fellow with the handle Mokus did a very, very tiny implementation for a microcontroller with only 64 bytes of RAM. He helped me modify his code so I could compare his statistics, and after adjustment his spectrum and distribution match fairly well. The high-frequency of his PSD looks a little different from the other methods, but these may not be noticeable to the observer. Finally, there was Eric Evenchick’s coincidental post on hackaday. Mokus reported that Evanchick’s implementation has too slow an update rate; I noticed that Evanchick did not report on the statistics he was targeting nor what he achieved. I did not recreate his work to test.

Then, on to the tests. I really was interested in building and comparing statistics from a 16 bit implementation, a 32 bit implementation in both a Direct Form I and a Direct Form II implementation. Indeed, I had great difficulty getting the filters to perform because I kept misdesigning the integer coefficients and overflowing the registers. As I sought a solution to the 2nd-order filter approach, I also created a 4-stage digital equivalent of an RC filter. The 4-stage RC approach was always stable though it needed a higher sample rate and used much more processor power to create statistically consistent results. On the other hand, it has a more accurate spectrum. A comparison of three different 16-bit methods to Mokus’ and to the actual measurements is shown in the figure below. The legend shows the mean, standard deviation, and their ratio to the right of the label. The All my filters did a credible job of reconstructing the histogram.

histo_compare_16

The power spectral density (PSD) of the different methods tells a different story. The Direct Form II 16 bit filter is the most visually appealing of the methods I tried. It rolls off more like the physical data than the other methods, except compared to the 4-stage RC filter. The Direct Form II filter is more computationally efficient.

psd_compare_16

The results for the 32-bit versions show greater variance than the 16-bit versions, but the quality is not markedly better.

histo_compare_32

psd_compare_32

 

I wrote a proof code for the Arduino UNO both to see it flicker and to test the processor speed—separate parts of the code. The results are that compiling with 1.0.3 resulted in a 4,722 byte program that calculated 10,000 new values in 6,292 ms, or 629 microseconds per value. In theory this could produce a sample rate of nearly 1.6 KHz. Or another way of thinking about this is that the final code uses about 629 us/17 ms or about 4% of the processor capability of the Arduino UNO. That leaves a lot of resources available to do other Arduino work or maybe means it can fit in a cheaper processor.

I have released two pieces of code under the GNU Public License 3, you can get the Python I used for filter design and the Arduino test code at the links. If you want the data, please contact me through the comments and I am willing to provide it.

Candle Flame Flicker

For a project I wanted to make an LED flicker like a candle. I searched for the signal statistics of candle flicker, and I found no data. One student web site suggests that candle flame flicker is a 1/f-type random signal with roll-off of 20 dB per decade increase in frequency. Similar processes are typical for turbulence, so this student’s plan seemed reasonable. However, the student did not discuss whether the signal is Gaussian or not, and did not describe the low-frequency characteristics of the signal. 1/f noises may have a spectrum that follows the 1/f curve to very low frequencies, but because they would require infinite power at f=0 they always have some lower frequency change. I had no data.

Candles aren’t hard to get, and I already had a silicon photodiode for an absorptive smoke density measurement system I’m working on. I also had an analog-to-digital converter (ADC) in an ADS1015 on a breakout board from Adafruit. I made the very simple circuit shown below and attached it to a Raspberry Pi to sample the data. There are a lot more details, but those are later.

circuit

The voltage measured by the ADC is directly proportional to the current through the resistor. The current through the reverse-biased diode is directly proportional to the incident optical power. Very simple. I recorded a minute of data at a low 250 Hz sample rate, and subjected the data to analysis. The setup was a nominally dark room with the sensor a few inches from the flame. I flapped my hand at the candle to get it to flicker while recording.

20131211-04

20131211-06

20131211-12

The first graph below is a histogram of sample values.

dfile_hist

The histogram is about normally distributed, but the right-hand tail is not Gaussian; it is too fat. In other words the candle is occasionally much brighter than normal. The time series (below) shows the same properties. There are clearly visible large excursions.

dfile_time

For human eyes the candle’s flicker will be well represented if the frequency spectrum of the flicker and the distribution of the flicker approximately match a natural source. The spectrum below can be thought of as an average brightness (the peak at the left), a flat spectral region out to about 4 Hz, and then a 1/f-style roll off at 44 dB per decade.

dfile_psd

Numerically, we have the recipe for a flickering candle:

  • Samples should be normally distributed with a standard deviation equal to 0.25 of the mean.
  • The power spectral density of the signal should roll off at about 40 dB per decade with a 3 dB cutoff frequency around six cycles per second.

To make this work on the Arduino using the pulse-width modulated outputs, we can further constrain the problem:

  • The maximum value cannot exceed 255 counts—or make the limit that the mean plus two standard deviations is 255.
  • From this, we can derive that 2s+m = 255, use the fact that 0.25m=s to find that the mean m=170 and the standard deviation is about 42.
  • A sample rate of between 30 and 120 Hz should be more than adequate to satisfy the Nyquist criterion for human vision (see Wikipedia).
  • Values may not go below zero or above 255
  • A second-order infinite impulse response (IIR) filter has a roll-off of 40 dB per decade

If we can find a numerically efficient way to generate a time-series of Gaussian random variables inside the Arduino, filter them with a 2nd-order fixed-point IIR, scale them (if needed) then we should be able to make a flickering candle.

Unfortunately, I have failed repeatedly to get a stable fixed point IIR filter. The cookbook solution specification above should be easy to implement, but I have not found it so. A better solution will have to wait for another post.

Pens for the Backs of Photographs, More Ink

I tested three new writing media for the backs of photographs. I recently went through some 2 or 3 year old pictures I had marked with Higgins Black Magic. In exactly one case I found one photo that had picked up pen marks from another. I do not know if I put them together while the ink was still wet, or if the ink adhered over time. I was displeased, though no harm was done to the pictures.

I suspect the cause is that Higgins Black Magic is a latex-based ink. Like latex paint in a house, it never fully loses its stickiness. I decided to round up a couple more candidates, and I have two new winners and a loser to add to the mix, and one more loser.

I bought a Copic Multiliner SP pen in 0.03 mm (very, very, fine line) and tried it. This pen uses a fiber-filled cartridge refill, so you can’t change the ink. As the unaltered scan shows, after one minute it smeared badly. After an hour or more it seems pretty stable, but it is such a light grey that it is miserable to read.

copic_multiliner_sp

The second test was a product labeled “Royal India Ink Encre de Chine” by Reeves & Poole Group. This smells like alcohol and is almost certainly a shellac-based product. Like Higgins Black Magic the Reeves & Poole leaves a slightly embossed feeling on the paper, but goodness it writes well on photo paper. I do not know if it is archival. Shellac cleans easily with denatured alcohol, which is cheap in a gallon drum from the home center. I doubt it would be safe in a technical pen.

reeves_and_pool_royal

The clear winner is the Rapidograph Black India Universal 3080-F.BLA ink, which left less embossed character on the photo paper, dried almost instantly, and is safe for technical pens. Or at least as safe as anything can be in a pen that requires cleaning. This ink may also be shellac based, it smells of a solvent that is more lacquer-like than latex-like. As with most other inks, I can find no data about archival quality.

The technical pen is much easier than a dip pen and inkwell when your desk is cluttered with photos you are scanning. I am pleased to report this is probably my new go-to ink for photo work.

universal_3080-F