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A Eulogy for the Headphone Jack

Sometime in the mid-2000s, I was a freelance web developer in Philadelphia with some pretty crappy health insurance. I started having occasional heart palpitations, like skipped heart beats. My doctor said it was probably not serious, but she could do tests to rule out very unlikely potential complications for about $1,000. That seemed pretty expensive to rent a portable EKG for a single day, so I googled around for some schematics. Turned out you could build a basic three-lead EKG with about $5 worth of Radio Shack parts (I no longer have the exact schematic, but something like this). I didn’t really understand what the circuit did, but I followed the directions and soldered it together on some protoboard, connected a 9V battery, and used three pennies as electrodes that I taped to my chest. I hooked the output of the device to my laptop’s line in and pressed ‘record’.

screenshot of my heartbeat in Audacity

Audacity displayed the heartbeat signal live as it recorded. Sure enough, I was having pretty common/harmless Premature Ventricular Contractions. There’s one on the right side of the screenshot above.

Calling the 1/8th inch connectors you’d find on pretty much every piece of consumer electronics until recently “audio jacks” does them a disservice. It’s like calling your car a “grocery machine”. Headphone and microphone ports are, at their most basic, tools for reading and producing voltages precisely and rapidly over time.

My homemade EKG is a voltage converter. Electrodes attached to points around my heart measure tiny differences in voltage produced by signals that keep it beating. Those measured signals are amplified to about plus or minus 2 volts. That new voltage travels through an audio cable to the “Line In” on my sound card.

Sound cards happen to carry sound most of the time, but they are perfectly happy measuring any AC voltage from -2 to +2 volts at 48,000 times per second with 16 bits of accuracy. Put another way, your microphone jack measures the voltage on a wire (two wires for stereo) every 0.02 milliseconds, and records it as a value between 0 and 65,535. Your headphone jack does the opposite, by applying a voltage between -2 and +2 to a wire every 0.2 milliseconds, it creates a sound.


To any headphone jack, all audio is raw in the sense that it exists as a series of voltages that ultimately began as measurements by some tool, like a microphone or an electric guitar pickup or an EKG. There is no encryption or rights management, no special encoding or secret keys. It’s just data in the shape of the sound itself, as a record of voltages over time. When you play back a sound file, you feed that record of voltages to your headphone jack. It applies those voltages to, say, the coil in your speaker, which then pushes or pulls against a permanent magnet to move the air in the same way it originally moved the microphone whenever the sound was recorded.

Smartphone manufacturers are broadly eliminating headphone jacks going forward, replacing them with wireless headphones or BlueTooth. We’re going to all lose touch with something, and to me it feels like something important.

The series of voltages a headphone jack creates is immediately understandable and usable with the most basic tools. If you coil up some copper, and put a magnet in the middle, and then hook each side of the coil up to your phone’s headphone jack, it would make sounds. They would not be pleasant or loud, but they would be tangible and human-scale and understandable. It’s a part of your phone that can read and produce electrical vibrations.

Without that port, we will forever be beholden to device drivers between our sounds and our speakers. We’ll lose reliable access to an analog voltage we could use to drive any magnetic coil on earth, any pair of headphones. Instead, we’ll have to pay a toll, either through dongles or wireless headphones. It will be the end of a common interface for sound transfer that survived more or less unchanged for a century, the end of plugging your iPod into any stereo bought since WWII.

Entrepreneurs and engineers will lose access to a nearly universal, license-free I/O port. Independent headphone manufacturers will be forced into a dongle-bound second-class citizenry. Companies like Square — which made brilliant use of the headphone/microphone jack to produce credit card readers that are cheap enough to just give away for free — will be hit with extra licensing fees.

Because a voltage is just a voltage. Beyond an input range, nobody can define what you do with it. In the case of the Square magstripe reader, it is powered by the energy generally used to drive speakers (harvesting the energy of a sine wave being played over the headphones), and it transmits data to the microphone input.

There’s also the HiJack project, which makes this whole repurposing process open source and general purpose. They provide circuits that cost less than $3 to build that can harvest 7mW of power from a sound playing out of an iPhone’s headphone jack. Because you have raw access to some hardware that reads and writes voltages, you can layer an API on top of it to do anything you want, and it’s not licensable or limited by outside interests, just some reasonably basic analog electronics.

I don’t know exactly how losing direct access to our signals will harm us, but doesn’t it feel like it’s going to somehow? Like we may get so far removed from how our devices work, by licenses and DRM, dongles and adapters that we no longer even want to understand them? There’s beauty in the transformation of sound waves to electricity through a microphone, and then from electricity back to sound again through a speaker coil. It is pleasant to understand. Compare that to understanding, say, the latest BlueTooth API. One’s an arbitrary and fleeting manmade abstraction, the other a mysterious and dazzlingly convenient property of the natural world.


So, if you’re like me and you like headphone jacks, what can you do? Well, you could only buy phones that have them, which I think you’ll be able to do for a couple years. Vote with your dollar!

You can also tell companies that are getting rid of headphone jacks that you don’t like it. That your mother did not raise a fool. That aside from maybe water-resistance, there’s not a single good reason you can think of to give up your headphone jack. Tell them you see what they’re up to, and you don’t like it. You can say this part slightly deeper, through gritted teeth, if you get to say it aloud. Or, just italicize it so they know you are serious.

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