Portable pcs have a standard ________-mm audio out port.

If you've ever plugged an older smartphone or portable music player into a car stereo, you've likely used an aux (auxiliary) cord to make the connection from the device's headphone jack to the car's aux input. If you've ever wondered if the names of these connectors are interchangeable, this article is for you.

Are AUX (Auxiliary) connectors & headphone jacks the same? The construction of the aux connector and the headphone jack is often the same: 3.5mm (1/8″) TRS. However, the “auxiliary connector” is universal for audio while the “headphone jack” is, by its name, suited for headphones. Headphone jacks also come in different sizes and wiring schemes.

In this article, we'll discuss headphone jacks and auxiliary connections in more detail, focusing on their similarities as well as their differences.

What Is A Headphone Jack?

As the name suggests, a headphone jack is a connection meant to send audio signals to headphones. The headphone jack is the female connection (at the audio source), while the headphone plug is the male connection (at the end of the headphone cable).

Headphone jacks generally have an output impedance of less than 24 Ω. Headphones typically have an impedance between 8 Ω to 600 Ω, with the 32 Ω standard becoming more common.

The signal from a headphone jack is often not strong enough to drive professional high-impedance headphones. In this case, a headphone amplifier is often required to boost the voltage and bridge the impedance between the audio source (now the amp) and the high-impedance headphones.

Headphone jacks come in a variety of sizes, described by their diameters. The sizes are:

• 2.5mm (3/32″)
• 3.5mm (1/8″)
• 4.4mm
• 6.35mm (1/4″)

The Rupert Neve Designs RNHP (link to check the price at B&H Photo/Video) is an excellent example of a headphone amplifier with a 6.35mm (1/4″) headphone output.

Rupert Neve Designs is featured in the following My New Microphone articles:
• Top 10 Best Studio Recording/Mixing Console Brands
• Top 11 Best Audio Compressor Brands In The World
• Top 11 Best Audio Equalizer Brands In The World
• Top 11 Best Audio Brands For 500 Series Modules/Equipment
• Top 11 Best Direct Inject Audio Box Brands On The Market

To learn more about headphone amplifiers, check out my article What Is A Headphone Amplifier & Are Headphone Amps Worth It?

Headphone jacks utilize tip, ring and sleeve connections (often referred to as poles). Each pole makes its own connection for carrying audio signals, and headphone jack designs vary with the number of poles. They include:

• TS (tip-sleeve)
• TRS (tip-ring-sleeve)
• TRRS (tip-ring-ring-sleeve)
• TRRRS (tip-ring-ring-ring-sleeve)

The most common headphone jack is the 3.5mm TRRS (think of laptops, tablets and older smartphones). Although the jack has full TRRS capabilities, it will likely work just fine with TRS and TS plugs (as well as TRRS plugs).

Note that there are different wiring standards when it comes to TRS, TRRS and TRRRS standards. We'll discuss these in greater detail in the section on wiring standards.

To learn more about headphone jacks and the various types of jack and plugs, check out my article Differences Between 2.5mm, 3.5mm & 6.35mm Headphone Jacks.

What Is An Aux Connection?

Auxiliary connections are designed to connect a wide variety of devices to a single quasi-universal jack.

You've likely seen an aux input in a 2000's car stereo. These inputs allow us to connect smartphones, mp3 players, laptops, and plenty of other devices directly into the car's audio system for playback.

Auxiliary inputs generally have an impedance of more than 10 kΩ and expect to receive a nominal voltage level of -10 dBV (0.300 VRMS). Again, the voltage level is highly dependent on the volume control of the audio device.

Aux inputs are always 3.5mm TRS unbalanced stereo.

Auxiliary inputs are often found in automobile stereo systems, stereo receivers; audio amplifiers; active loudspeakers, and even clock radios.

The Boss Audio Systems 508UAB (link to check the price at Boss Audio) is a great example of a multimedia automobile stereo with an auxiliary input (to the bottom right corner).

Boss Audio Systems is featured in the following My New Microphone articles:
• Top 9 Best Car Stereo Brands In The World
• Top 11 Best Car Audio Speaker Brands In The World
• Top 11 Best Car Audio Amplifier Brands In The World

While dedicated auxiliary outputs are generally only found on mixing consoles, the aux input connection is designed to accept a wide variety of audio sources. This means that although headphone outputs and line outputs are not “aux outputs,” they are still compatible with auxiliary inputs.

Auxiliary outputs generally have an impedance of 75Ω to 150 Ω and a nominal voltage level of -10 dBV (0.300 VRMS). However, the voltage level is highly dependent on the volume control of the device.

Aux outputs are similar to line outputs and are often used to send an additional output from a stereo amplifier or mixing console to a separate recording device.

The Yamaha MG10 (link to compare price on Amazon and B&H Photo/Video) is a nifty little mixer with an auxiliary output (line level) and a headphone output.

The light blue pots/knobs in each channel adjust the channel's pre-fader level in the aux output. This aux output is 1/4″ 6.35mm TRS unbalanced stereo at line level.

The headphone output is also unbalanced stereo with a 6.35mm 1/4″ TRS jack.

Both these jacks are found in the top right corner.

Auxiliary sends are commonly used in bigger mixing consoles. These aux sends allow for alternative mixes within a mixing console and are often used to feed different monitors mixes for different musicians on stage or to feed external recorders. These aux sends generally output line level signals (+4 dBu (1.228 VRMS) with 75 to 600 Ω).

The Similarities Between Headphone & Aux Inputs/Outputs

Before we get into the differences, let's touch on the similarities between the headphone and aux jacks/plugs.

Let's begin by stating that both headphone and aux connections are analog. This means that the audio signals are electrical AC voltages that travel through conductive wires in a cable.

That being said, due to the digital nature of many audio devices, there are often analog-to-digital converters immediately at the jacks of both headphone and auxiliary ports.

For example, the audio being played within a smartphone is digital and must be converted to analog audio before being outputted from the headphone jack. Let's say the analog signal is sent to a car stereo. There is an analog-to-digital converter at the aux input to convert the audio beck to digital for use in the car's stereo. The audio is converted once again to analog at the amplifier to drive the car's speakers properly.

Another similarity between aux and headphone jacks/plugs is their size, wiring and aesthetic. This is why they so often get confused.

The headphone output of a smartphone or laptop looks the same as the auxiliary input of a car stereo. What's the deal?

As mentioned previously, the auxiliary input is designed as a sort of universal plug that accepts various audio sources. The 3.5mm TRS connector seems the most compatible.

Although headphone jacks vary widely in size and wiring, the 3.5mm TRS and 3.5mm TRRS are the most common.

A simple male-to-male 3.5mm TRS or TRRS “aux cable” will effectively connect most consumer audio devices to an aux input.

There are plenty of 3.5mm TRS aux cables on the market. Check out the AmazonBasics Audio Aux Cable, for example.

Aux inputs will accept headphone level signals and other “types” of audio signals with varying voltage and impedance levels.

The Differences Between Headphone & Aux Inputs/Outputs

Aux outputs have relatively low-level signals that are designed to drive fairly high-impedance loads. Most commercially available headphones have a much lower impedance than the aux out is designed to drive. This will result in a fairly weak signal, and it may be distorted.

If you're trying to send an audio signal from an aux output to a pair of headphones, I'd suggest using a headphone amplifier in-inline between the two.

This is to say that a major difference between aux and headphone jacks/plugs is that a headphone output can effectively send a signal to an aux input, but an aux output has some difficulty a signal to a headphone “input.”

This is largely due to the contrasting voltages and impedances between the two:

• Aux inputs have 10 kΩ impedance while aux outputs have 75 Ω to 150 Ω impedance. The outputs have a nominal voltage level of -10 dBV (0.300 VRMS).
• Headphone inputs have 8 Ω to 600 Ω impedance while headphone output jacks have 0.1 Ω to <24 Ω impedance. Headphone amps help to boost impedance up to 0.5 Ω to 50 Ω. The voltage is highly dependent on the type of headphone driver and the impedance of the headphones (higher impedances require higher voltages for the necessary current).

To get a better understanding of impedance and headphones, check out my article The Complete Guide To Understanding Headphone Impedance.

Another big difference between the headphone and aux plugs/jacks is the variety in size and wiring of headphone jacks versus the one-size-fits-all approach of the aux input.

As we've discussed earlier, headphone connections come in an assortment of sizes (2.5mm, 3.5mm, 4.4mm and 6.35mm) and have many different wiring standards.

For more information on the sizes of headphone plugs and jacks, check out my article The Differences Between 2.5mm, 3.5mm & 6.35mm Headphone Jacks.

Aux inputs connectors are nearly always 3.5mm unbalanced TRS that can accept TRRS.

Aux outputs can be either balanced mono or unbalanced stereo. Aux send line outputs sometimes have a single TRS connector which can be wired as balanced mono (rare) or unbalanced stereo (common).

Aux send line outputs may also have two separate connectors for balanced left channel audio and balanced right channel audio. These outputs are generally added together to a pair of headphones or used to drive a pair of loudspeakers/monitors.

3.5mm headphone connections are generally always stereo unbalanced.

I'm using phrases like “nearly always,” “generally,” and “typically” because there is a lot of variation in the wiring standards of headphone connections (and some variation in aux outputs as well). This brings us to our next point.

Some audio playback devices, like many smartphones, don't even have headphone outputs.

To learn more about connecting headphones without a proper jack, check out my article How To Connect Headphones To A Smartphone With No Jack.

Wiring Standards

Let's quickly run through the numerous wiring standards of headphone and aux connections to understand their similarities and differences better. We'll start with the aux connectors.

Aux Input Wiring Standards

The aux input is a 3.5mm TRS (tip-ring-sleeve) connection that accepts unbalanced stereo audio from TRS and TRRS cables.

Its wiring is as follows:

• Tip: left channel audio
• Ring: right channel audio
• Sleeve: common ground

This allows the aux input to accept stereo signals from other devices with ease. Note that the TRRS signals from headset-type headphones can effectively connect to the TRS aux input. The tip and first ring of the TRRS will effectively connect the left and right audio channels (to the tip and ring of the TRS). The microphone (on the second ring or sleeve, depending on the wiring standard) will be sent to the ground (the sleeve of the TRS). This allows full compatibility between aux input and smartphones, laptops and tablets.

Aux Output Wiring Standards

The aux outputs of a mixer or amp have two main wiring standards:

The first is the unbalanced stereo TRS:

• Tip: left channel audio
• Ring: right channel audio
• Sleeve: common ground

This connection is typically used to drive headphones or a stereo line input. A “Y-cable” can be used to split the connector into two individual unbalanced signals. This is generally done by splitting into two unbalanced RCA connectors though the split could also go to two TS.

The second is the balanced mono TRS:

• Tip: audio signal (positive polarity)
• Ring: audio signal (negative polarity)
• Sleeve: common ground

Typically these balanced aux outputs will be in pairs with a left channel aux out and a right channel aux output. These sends are generally sent to a stereo pair of auxiliary monitors or loudspeakers.

Auxiliary sends/outputs generally utilize 6.35mm (1/4″) jacks/plugs.

Headphone Jack/Plug Wiring Standards

Compatible headphone jacks and plugs have the same potential wiring standards. In this section, I'll discuss the plug since they're easier to see but know that the jacks can have the same wiring. When necessary, I'll share the compatibilities and incompatibilities between the jacks and plugs.

TS Headphone Jacks/Plugs

The TS connector yields unbalanced mono. It is the simplest type of headphone connector and is typically found in 2.5mm headphone jacks/plugs.

The unbalanced mono TS headphone jack/plug is wired as follows:

• Tip: audio
• Sleeve: return path + ground

Note that the TS 1/4″ (6.35mm) jack is often used for electric instruments like electric guitar and bass. In these cases, it is commonly referred to as a patch cord.

Headphone amps often utilize 6.35mm jacks but are designed as TRS to send stereo signals to professional high-impedance headphones. Speaking of TRS, let's move on.

TRS Headphone Jacks/Plugs

The TRS headphone jack/plug is the most common and is the simplest way to provide unbalanced stereo audio to headphones.

The unbalanced stereo TRS headphone jack/plug is wired as follows:

• Tip: left channel audio
• Ring: right channel audio
• Sleeve: common ground

At the Y-split in the headphones, the tip goes to the left driver; the ring goes to the right driver, and the sleeve splits and goes to both drivers. This split effectively forms an unbalanced mono signal with each driver and offers the stereo image for the pair of headphones.

Note that, although aux sends/outputs may have balanced mono TRS, this is rarely the case with headphones since they are, for the most part, stereo. If a manufacturer is going to produce mono headphones, the connection will generally be unbalanced TS rather than balanced TRS. These mono headphones will accept mono signals from mono jacks or the left channel only from stereo jacks.

TRRS Headphone Jacks/Plugs

TRRS headphones jacks and plugs are generally used for headsets.

AHJ (CTIA) Standard

AHJ (American Headset Jack) standard of the CTIA is the new standard adopted by practically all producers of consumer-grade audio devices since 2015. Smartphone, laptop and tablet manufacturers have adopted the standard for a more unified and universal headphone-to-device connection.

The AHJ (CTIA) wiring standard is as follows:

• Tip: left channel audio
• Ring: right channel audio
• Ring: common ground
• Sleeve: microphone

OMTP Standard

OMTP (Open Mobile Terminal Platform) is an older standard that has been practically rendered obsolete by the aforementioned CTIA standard.

The OMTP wiring standard is as follows:

• Tip: left channel audio
• Ring: right channel audio
• Ring: microphone
• Sleeve: common ground

I've added the OMTP standard for your information if you happen to be using a TRRS headset and device that pre-date 2015.

Note that TRS headphones can and often do plug into TRRS jacks, and TRRS headphones can plug into TRS jacks, even though they are not considered fully compatible. Let's start with the first scenario and discuss the unbalanced TRS and CTIA standard TRRS:

A TRS plug's tip, ring and sleeve will properly connect to the tip, ring and second ring of a TRRS jack, respectively. The sleeve of the TRRS plug that is expecting a mic signal will be connected to the ground and will be effectively nullified.

A TRRS plug will connect similarly to a TRS jack though the microphone will be lost. The tip (left headphone audio), ring (right headphone audio) and second ring (ground) will properly connect to their respective tip, ring and sleeve in the TRS jack. The microphone (on the sleeve of the TRRS) will be sent to ground and not be properly transmitted.

Fortunately, most modern consumer-grade audio devices that have headphone jacks are wired as TRRS with the AHJ (CTIA) standard. They can, therefore, accept headsets without issue.

TRRRS Headphone Jacks/Plugs

The TRRRS (tip-ring-ring-ring-sleeve) headphone connections are relatively new and most often used with the 4.4mm Pentaconn connection.

This wiring scheme delivers balanced stereo audio to the headphones.

The 4.4mm Pentaconn TRRRS uses the following wiring scheme:

• Tip: left channel audio (positive polarity)
• Ring: left channel audio (negative polarity)
• Ring: right channel audio (positive polarity)
• Ring: right channel audio (negative polarity)
• Sleeve: ground/shield

This standard sends a balanced audio signal to the left headphone driver and the right headphone driver for perfectly balanced stereo audio. Balanced audio has good signal strength, is less prone to electromagnetic interference, and is capable of travelling through longer cable lengths than unbalanced audio. In theory, the balanced TRRRS stereo headphone standard will outperform the unbalanced TRS stereo headphone standard.

For more information on balanced and unbalanced audio, check out my article Do Microphones Output Balanced Or Unbalanced Audio?

The Headphone Amplifier

Since headphone amplifiers have been brought up so much in this article, I figured I'd give them their own section.

A headphone amplifier is a device that applies gain (amplifies) to an audio signal and converts its impedance to best suit a pair of headphones.

The headphone jacks in our smartphones, laptops, and etcetera have tiny headphone amps included in their digital-to-analog converters. These amps allow our consumer-grade devices to drive most earbuds and headphones properly.

However, many professional headphones (and many planar magnetic and electrostatic headphones) have higher impedances and require an external amplifier to properly drive their drivers with the appropriate current. At higher impedances, this means greater voltages.

Note that, at one time, it was once common to assume that the higher their impedance, the best quality the headphones.

Since the explosion in popularity of portable audio players, headphone manufacturers have adapted, and not there are plenty of high-quality low-impedance headphones on the market. That being said, we can bet that high-impedance headphones will sound amazing if connected to a proper headphone amp.

So external headphone amps effectively supply the necessary voltage to drive the high impedance of many professional headphones.

The high impedance of moving-coil dynamic headphones allows them to deliver more precision by using more coils in their drivers. The result is a clearer, more powerful and more accurate sound.

To learn more about dynamic headphones, check out my article What Are Dynamic Headphones And How Do They Work?

An electrostatic pair of headphones requires extremely high voltages and very little current to charge the stators on either side of its diaphragm. Electrostatic headphones are known for being incredibly realistic and accurate. Non-electret electrostatic headphones also require DC biasing from an external power source (included in their specialized amplifiers).

To learn more about headphones and their power requirements, check out my article How Do Headphones Get Power & Why Do They Need Power?

Planar magnetic headphones generally have lower impedance values but still benefit from the boosted voltage provided by conventional headphone amplifiers.

Can I use a headphone jack as line out? Though headphone outputs and line outputs are different, headphone outputs can (and sometimes do) drive line level inputs designed to receive line level signals. The main difference is in the impedance: line level inputs have 10 kΩ to 50 kΩ impedance and expect 75 to 600 Ω source (line output) impedance while headphones have 8 Ω to 500 Ω impedance and expect a 0.1 Ω to 50 Ω source.

How many types of headphone jacks are there? There are 4 noteworthy standardized headphone jack/plug sizes: 3 are common (2.5mm, 3.5mm, 6.35mm), and one is quite rare (4.4mm). The 3 common types range in wiring standards with TS, TRS and TRRS wiring schemes. The 4.4mm jack nearly always utilizes a TRRRS wiring scheme. T = tip; R = ring, S = sleeve.