Connecting a guitar, bass guitar, synthesizer, keyboard (and many other instruments) to their respective amplifier is often as easy as plugging one end of a patch cable into the instrument and the other end into the amp. If you've ever wondered how this simple set up works on a more technical level, this article is for you! How do patch cables carry audio? Patch cables, AKA patch cords or 1/4" (6.35mm) TS (tip-sleeve) cables, are unbalanced cables that carry unbalanced audio signals from one male end to the other male end. There are two conductors in the cable: one carries the signal and the other acts as a shield and return path for the signal. In this article, we'll discuss patch cables in greater detail; how they carry audio from our instruments, and how to get the best results out of our patch cables. Table Of Contents What Is A Patch Cable?Unbalanced Audio Vs. Balanced AudioUnbalanced AudioBalanced AudioThe Outputs Of Various InstrumentsThe Inputs Of Headphones And LoudspeakersThe Inputs And Outputs Of Other Audio DevicesPatch Cables For Guitar And BassPatch Cables For Keyboards-And-SynthesizersPatch Cables For MicrophonesPatch Cables For HeadphonesPatch Cables For LoudspeakersWhat About Patch Bay Cables?Patch Cables For Eurorack & Modular SynthsRelated Questions What Is A Patch Cable? Before we get too far into this article, let's define the term "patch cable". Patch cables (or patch cords) are generally what musicians call the 1/4" cables that connect their instruments to their amplifiers or to mixing boards. For guitarists and bassists, these patch cables are generally between 10 to 25 feet long and have TS (tip-sleeve) male connectors at each end. For many of us guitarists (myself included), this is the definition of "patch cable". But that's not technically correct. As guitarists, we use 1/4" TS cables as our patch cords and so they are what we know to be patch cords but the term is actually much broader than that. A patch cable is defined as any electrical (or optical) used to connect or "patch" one electronic (or optical) device to another. So, then any signal carrying cable in audio, even the XLR microphone cables, are technically "patch cords". Related article: Why Do Microphones Use XLR Cables? By that definition, the balanced 1/4" TRS cables that carry audio from the [sometimes] balanced outputs of synthesizers are also patch cables. So, too, are the mic cables that carry audio from a microphone to a preamp; the unbalanced TRS 3.5mm (1/8") cables that carry audio from a playback device to our headphones, and every other cable that carries audio from one device to another. In this article, we'll focus on the patch cables that carry audio from the following instruments: Guitars and bass guitarsKeyboards and synthesizersMicrophones We'll also talk briefly about the patch cables used to bring audio to headphones and loudspeakers. There is, of course, much more to cover than this article will get into. I'll link to other My New Microphone articles along the way to provide additional resources to further your knowledge. Covering patch cables in the scenarios mentioned above will give us a solid understanding of the how patch cables carry audio. Unbalanced Audio Vs. Balanced Audio To really understand how patch cables carry audio, we must understand the difference between unbalanced and balanced audio transfer. This is a major differentiator in the design and performance of an audio cable. Unbalanced Audio What is unbalanced audio? Unbalanced audio is a system of carrying audio on two conductive wires within a cable. The signal wire carries the audio signal while the shield/ground wire acts as a return path to complete circuit; a shield from electromagnetic interference, and a ground wire if need be. An unbalanced cable will tend to have the signal wire at the centre of its cross-section. There will be some insulation between the signal wire and the cylindrical frayed return/shield/ground "wire". There will be more insulation and the outer protective layer at the outside of the connector. So unbalanced cables only use two conductors. The ground wire simultaneously shields the signal wire from electromagnetic interference (EMI) noise and acts as an antenna, which picks up EMI noise. Any noise picked up by an unbalanced cable is subjected to the audio signal. The more noise the unbalanced line induces, the worse the signal-to-noise ratio of the audio signal. Having two conductors separated by insulation like this produces capacitance as well. The unbalanced cable conductors act a capacitor along the entire length of the cable and produce distributed capacitance. This means that longer cables will have more capacitance. Unfortunately, having capacitance in a cable causes a low-pass filter effect. The more capacitance (longer cable) causes a lower cutoff frequency for this filter. This is why it's important to use shorter unbalanced patch cables in our systems. This is particularly true with guitar, bass guitar and some synthesizers. Unbalanced cables/connections include: Tip-Sleeve (TS): In Tip-Sleeve (TS) connectors, the tip is the signal wire and the sleeve is the ground wire.Unbalanced stereo Tip-Ring-Sleeve: Unbalanced stereo TRS has the unbalanced left audio channel on the tip, unbalanced right audio channel on the ring, and a common ground wire on the sleeve.Unbalanced mono Tip-Ring-Sleeve with DC bias: Some microphones (particularly lavaliers) require a DC bias voltage in order to function properly. TRS with DC bias has the tip as signal wire, the ring as DC bias wire, and the sleeve as the ground wire.Tip-Ring-Ring-Sleeve (OMTP standard): This “old” standard carried an unbalanced headset signal with the following wiring: Tip is for unbalanced headphone right audio channel, Ring 1 is for unbalanced headphone right audio channel, Ring 2 is for unbalanced microphone audio, and Sleeve is for ground.Tip-Ring-Ring-Sleeve (CTIA/AHJ standard): This “new” standard carries an unbalanced headset signal with the following wiring: Tip is for unbalanced headphone right audio channel, Ring 1 is for unbalanced headphone right audio channel, Ring 2 is for ground, and Sleeve is for unbalanced microphone audio.RCA: RCA has an inner pin that carries the audio signal and an outer shield that acts as the ground/shield/signal return wire. Let's focus on the TS connectors for a moment. We'll start with a picture of the typical 1/4" (6.35mm) TS cable used for guitars, bass guitar and many synthesizers and keyboards: 1/4" (6.35mm) TS Male Connector Look familiar? This phono connector is used to connect guitars, bass guitars, effects pedals, synthesizers, keyboards and even some microphones and other instruments. Let's have a look at a simplified schematic of the unbalanced connection: Basic Unbalanced Mono Audio Schematic As we can see, the signal is carried by the signal and return wires. The return/shield does block some EMI but, ultimately, noise will get into the signal. The noise in the illustration above is overstated just to show that there will be some noise. Either end of the unbalanced cable can be connected to ground if need be. This is sometimes the case at the mixer or amplifier end rather than the instrument end. Balanced Audio What is balanced audio? Balanced audio is a system of carrying audio using three conductive wires within a cable. Two signal wires carry the same signal in opposite polarities and are both relative to the ground/shield wire (which doesn't carry signal). Balanced audio inputs require a differential amplifier to sum the differences between the signal wires to effectively use the signal. So balanced audio requires three wires to function properly. The same signal is present in positive polarity on the hot/positive wire and negative polarity on the cold/negative wire. Each signal wire is referenced to a third wire that acts as a common ground. The ground wire simultaneously shields the signal wires from EMI noise and acts as an antenna, which picks up EMI noise. Overall, the insulation and ground/shield wire reduce the amount of noise that is transferred to each of the signal wires. A common design feature of balanced cables is the interweaving of the two signal wires into what is known as a twisted pair. A twisted pair of signal wires makes the induced noise more evenly distributed between the two signal wires. So basically what ends up happening is the two signal wires end up with equal amounts of signal interference noise in the same polarity, but the signals are in opposite polarity. When the balanced line is sent to a balanced input, a differential amplifier sums the differences between the two signal wires. This rids of the noise (which is the same on each wire) and adds the signals together (which are completely “out-of-phase” with one another). This process is known as common-mode rejection. With common-mode rejection, we may run long balanced audio lines with little degradation in the audio signal due to noise or distributed capacitance! Some synthesizers utilize balanced outputs. Professional microphones always use balanced audio. Related article: Do Microphones Output Balanced Or Unbalanced Audio? Balanced cables/connections include: 3-pin XLR: In XLR connectors, which are the standard for carrying balanced microphone audio, pin 1 is the ground wire, pin 2 is the positive audio wire, and pin 3 is the negative audio wire.Balanced Tip-Ring-Sleeve: In the balanced mono version of TRS, which isn’t very common for microphones (though XLR-balanced TRS adapters do exist), the tip is the positive audio wire, the ring is the negative audio wire, and the sleeve is the ground wire. Let's have a look at the TRS connectors for a moment. We'll start with a picture of the typical 1/4" (6.35mm) TRS cable used for some synthesizers and keyboards: 1/4" (6.35mm) TRS Male Connector We see here that the ring provides an additional connection that coincides with the "negative polarity" signal wire within the cable. Let's have a look at a simplified schematic of the balanced connection: Basic Balanced Mono Audio Schematic We see above that the two signals are the same but in opposite polarity and that the ground wire does not carry a signal. Noise will inevitably get on the signal wires. However, the noise, in a proper balanced cable, should be the same on each signal wire. Remember that the balanced input has a differential amplifier. This amp sums up the difference between the two signal wires, effectively cancelling out the noise and preserving the full signal. In fact, the signal is even twice as strong due to the summing of two identical waveforms! Now that we know about balanced and unbalanced audio, let's get into the patch cables used in our typical instruments! The Outputs Of Various Instruments Patch cables connect the outputs of certain audio devices to the inputs of others. It's important, then, to understand the nature of the outputs of various instruments and sound sources! Let's have a look at short table that lays out the output characteristics of various sources: Instrument OutputMono/StereoUnbalanced/BalancedTypical ImpedanceTypical Level Electric GuitarMonoUnbalanced7 - 15 kΩInstrument Level -20 dBu nominal Electric Bass GuitarMonoUnbalanced7 - 15 kΩInstrument Level: -20 dBu nominal Electric KeyboardMono or Stereo (dual mono)Unbalanced or Balanced10 - 15 kΩLine Level: +4 dBu nominal or -10 dBV nominal SynthesizerMono or Stereo (dual mono)Unbalanced or Balanced10 - 15 kΩLine Level: +4 dBu nominal or -10 dBV nominal MicrophoneMono or Stereo (dual mono)Typically Balanced50 - 600 ΩMic level: -60 dBV to -20 dBV nominal The table above gives us some hints as to the type of cable required to carry audio from the various instruments/sources. It also gives us some insight into the signal characteristics, which are good to know but not as important and the mono/stereo and unbalanced/balanced info. If you're interested in learning more about decibels in terms of audio (dB, dBV, dBu and more), check out my article What Are Decibels? The Ultimate dB Guide For Audio & Sound. The Inputs Of Headphones And Loudspeakers For playback, signals are typically patched into headphones and/or loudspeakers. Let's have a look at their input characteristics in the table below: TransducerMono/StereoUnbalanced/BalancedTypical ImpedanceTypical Level HeadphonesTypically StereoTypically Unbalanced10 - 300 Ω range nominalHeadphone/Line Level: -10 dBV nominal LoudspeakerMonoUnbalanced1 - 16 Ω nominalSpeaker Level: 0 dBV to 40 dBV nominal Related article: How Do Speakers & Headphones Work As Transducers? The Inputs And Outputs Of Other Audio Devices Of course, our understanding wouldn't be complete without knowing the characteristics of other I/O devices such as mixers, amplifiers, etc. Let's have a look at different inputs and outputs and how they are set up: I/O TypeMono/StereoUnbalanced/BalancedTypical ImpedanceTypical Level Mic InputMonoXLR: balanced1.5 to 15 kΩMic level: -60 dBV to -20 dBV nominal Line Input (Consumer)MonoTS: unbalanced RCA: unbalanced TRS: balanced10 kΩ to 50 kΩLine Level: -10 dBV nominal Line Output (Consumer)MonoTS: unbalanced RCA: unbalanced TRS: balanced75 to 600 ΩLine Level: -10 dBV nominal Line Input (Professional)MonoTS: unbalanced RCA: unbalanced TRS: balanced10 kΩ to 50 kΩLine Level: +4 dBu nominal Line Output (Professional)MonoTS: unbalanced RCA: unbalanced TRS: balanced75 to 600 ΩLine Level: +4 dBu nominal Instrument InputMono or StereoTS: unbalanced TRS: balanced XLR: balanced47 kΩ to over 10 MΩInstrument Level: -20 dBu nominal Headphone OutputStereoTRS: unbalanced (stereo)0.1 Ω to >120 ΩHeadphone level: -20 dBV nominal Speaker OutputMonoMost connectors: unbalanced
