The digital age has brought with it digital audio and an incredible variety of new audio devices. Headphones have become increasingly popular with the invention of the portable music player and are used in our daily lives to playback audio from our many digital audio devices.
Are headphones analog or digital audio devices? Though headphones are regularly connected to digital audio sources, they are innately analog devices. Headphone transducers convert continuously variable (analog) audio signals (electrical energy) into sound waves (mechanical wave energy) and often require a digital-to-analog converter to function.
In this article, we’ll explain the analog nature of headphones in more detail; have a look at how headphones effectively produce sound from digital audio, and discuss the differences between analog and digital audio.
Analog Vs. Digital Audio
Before we can really understand the analog nature of headphones, we should comprehend the differences between analog and digital audio.
First, let’s define audio simply as a represenation of sound.
What is sound?
Sound itself is made of mechanical wave energy. Sound waves in the audible range of human hearing oscillate in the range of 20 Hz – 20,000 Hz.
The mechanical waves of sound affect the localized pressure variation from the ambient pressure in a medium. They are a continuously variable physical quantity.
The term “analog” refers to measurements and representations of continuously variable physical quantities.
So, then, while sound is a continuously variable measurement of pressure in a medium, analog audio is a representation of this varying pressure in the form of electrical energy (voltage).
Because sound is defined within the frequency range of 20 Hz – 20,000 Hz, analog audio is defined within the same range.
Let’s have a look at the similarities between sound and analog audio. For this example, we’ll take a 1 kHz (1,000 Hz) sine wave that completes one cycle every millisecond.
As we see in the sound wave pictured below, we have a single wave cycle happening in 1 ms. The amplitude of the wave is measured in pressure deviation from the ambient pressure of the medium and can be given in pressure units (often in the SI unit Pascal) or in the units of decibels of sound pressure level (dB SPL).
The wave reaches a peak of maximum pressure (max. compression) and a trough of minimum pressure (max. rarefaction).
Any part of the wave above the dotted centre line represents an increase in localaized pressure compare to the ambient pressure. Any part of the wave below the dotted centre line represents a decrease in localized pressure.
If we have a look at a 1 kHz sine wave analog audio signal, we’ll see a striking similarity to the 1 kHz sound wave it represents.
The difference between the analog audio signal and the sound wave it represents is the type of energy they’re made of.
Sound is made of mechanical wave energy and is measured in pressure. Audio is made of electrical energy and its amplitude is measure in voltage.
Like the sound wave it represents, the analog audio signal has a peak and trough in each of its cycles.
The peak represents maximum positive voltage and forward flowing current. The trough represents maximum negative voltage and backward flowing current.
Any part of the wave above the dotted centre line represents positive voltage and forward-flowing electrical current. Any part of the wave below the dotted centre line represents negative voltage and backward-flowing electrical current.
The key takeaway is that both sound and analog signals are continuously variable.
To learn more about the relationship between sound and audio, check out my article What Is The Difference Between Sound And Audio?
Now let’s discuss digital audio.
Digital audio is effectively a representation of analog audio in a digital format. Rather than being continuously variable, digital audio takes samples or “snapshots” of the audio across time and assigns an amplitude to each sample.
The number of samples per second in digital audio is referred to as the sample rate. Two common sample rates are:
- 44.1 kHz (44,100 samples per second)
- 48 kHz (48,000 samples per second)
The number of potential amplitudes each sample can have is defined by the bit-depth of the digital audio signal.
Bit-depth is not linear like sample rate but is exponential. For each additional bit in a signal’s bit-depth, there is an additional 1 or 0 in a chain of 1s and 0s.
1-bit has two potential values: 1 or 0
2-bit has 4 potential values: 00; 01; 10, or 11
3-bit has 8 potential values: 000; 001; 010; 011; 100; 101; 110; 111
So on and so forth.
The two most common digital audio bit-depths are:
- 16-bit (216 or 65,536 distinct amplitude values)
- 24-bit (224 or 16,777,216 distinct amplitude values)
The same 1 kHz sine wave in digital audio (at 48 kHz 24-bit resolution) would look something like this:
The dotted line represents the intended analog signal. The bars represent the digital samples and the amplitudes of the samples.
So digital audio is non-continuous. It closely approximates analog but has discrete values.
Digital audio is great but it cannot be used to drive headphone drivers/transducers!
The Headphone Driver/Transducer
The headphone drivers are the most important elements in headphone design. They are the transducer elements responsible for converting audio signals (electrical energy) into sound waves (mechanical wave energy).
In order for the headphone drivers to work properly, they must be part of a circuit that passes an analog audio signal. These signals pass alternating current through some sort of conductor that causes the headphone diaphragm to oscillate back and forth.
Digital audio is not a continuous alternating current and will not drive a headphone driver.
To learn more about headphone drivers, check out my article What Is A Headphone Driver? (How All 5 Driver Types Work).
Digital-To-Analog Converters (DACs)
So if digital audio cannot drive headphones, how do headphones connect to digital audio devices and effectively produce sound?
In order for a headphone to work with a digital audio source, the digital signal must pass through a digital-to-analog converter (DAC).
Digital-to-analog converters are put in-line between the digital audio source and the headphones. As their name suggests, they are devices that convert digital audio signals into analog audio signals.
DACs can be found in the following:
- Headphone jacks of digital audio devices (CD players, mp3 players, laptops, smartphones, tablets, etc.)
- Standalone adapters
- Headphone amplifiers and audio interfaces
- Digital mixing consoles
- Headphones (especially Bluetooth wireless headphones)
For more information on headphones and how they relate to computers, check out my article Are Headphones Input Or Output Devices?
Let’s briefly discuss each of the common digital-to-analog converters used to connect digital audio sources to headphones.
DACs In Headphone Jacks
A typical headphone jack in a smartphone, laptop, mp3 player or other digital audio device is designed with a built-in DAC. These DACs are considered part of the computer sound card.
The quality of there DACs varies widely and many of these devices will benefit from an upgraded external DAC. External DACs can come in the form of adapters; can be found in standalone devices, and can even be found built into the bodies of certain headphone models.
To learn more about headphone jacks, check out the following My New Microphone articles:
• How Do Headphone Jacks And Plugs Work? (+ Wiring Diagrams)
• Are AUX (Auxiliary) Connectors & Headphone Jacks The Same?
• Differences Between 2.5mm, 3.5mm & 6.35mm Headphone Jacks
There are many adapters that convert digital audio to analog audio with greater quality than the built-in DAC of regular headphone jacks.
If we remove the headphone amplfiers and interfaces from the equation (we’ll get to these shortly), we’re left with fairly simple digital-to-analog converters.
Let’s have a look at some simple adapter-style DACs.
The iBasso DC02 USB-C to 3.5mm (link to check the price at B&H Photo/Video) is a digital-to-analog converter and adapter between a USB-C digital connection and 3.5mm analog headphone jack connection. It can convert up to 32-Bit / 384 kHz digital audio resolutions.
The AudioQuest Dragonfly Cobalt (link to compare prices on Amazon and B&H Photo/Video) is a DAC + Preamp + Headphone Amp that connects via USB-A or USB-C (via an included adapter). This flash drive-sized DAC (ESS ES9038Q2M) has a native resolution up to 24-bit / 96kHz and provides incredible clarity and amplification to best suit our high-end headphones. Its headphone jack is sized at 3.5mm.
DACs In Headphone Amplifiers & Audio Interfaces
Headphone amplifiers often connect to digital devices via digital connections. Because these amps are designed to receive digital audio at their inputs, they will also have DACs with their amplifier circuits to effectively drive the headphones connected to their outputs.
The DACs in headphone amps are nearly always a step-up from the built-in DACs of typical headphone jacks.
Let’s now have a look at a few examples of headphone amplifiers with DACs.
The Fiio K3 (link to compare prices on Amazon and B&H Photo/Video) is a headphone amplifier with a built-in XMOS XUF208 DAC that connects to digital devices via USB-C. It features two different headphone outputs (a 3.5 mm (1/8″) single-ended jack and 2.5 mm TRRS balanced jack). It is capable of decoding up to 384kHz/32 bit PCM.
The SPL Phonitor xe (link to check the price at B&H Photo/Video) is a high-end audiophile headphone amplifier. In addition to its professional-grade analog inputs, it also has various digital input options:
- Coaxial input
- 1 Optical input
- USB Type-B input
- 1 AES XLR input
Its internal DAC is the SPL DAC768 (based on AKM AK4490) and has a 32-bit resolution.
For more information on headphone amplifiers, check out my article What Is A Headphone Amplifier & Are Headphone Amps Worth It?
Audio interfaces are central to many digital audio studio setups. They are fairly involved with both DACs and ADCs (analog-to-digital converters) and act to connect various audio devices to a computer.
Interfaces allow microphones, instruments, headphones, studio monitors, and other inherently analog audio devices to connect to computers. Audio interfaces work to connect input and output devices to computers.
The Focusrite Scarlett 2i2 (link to compare price on Amazon and B&H Photo/Video) is a popular audio interface for the project studio. It has internal DA and AD converters that support resolutions up to 192 kHz / 24-Bit. The 2i2 has a single headphone output.
Digital Mixing Console DACs
Mixing consoles and recording devices tend to have headphone outputs. Digital mixing consoles are no different.
However, because digital mixing consoles deal with digital audio, any outputs must have a digital-to-analog converter. This is the case with the headphone outputs in digital mixing consoles.
Built-In Headphone DACs
Wireless headphones that accept digital audio signals must have built-in DACs to convert the digital audio to analog audio that can driver the headphoens drivers. This is the case with Bluetooth headphones that have built-in DACs and amplifiers to accept digital audio, convert it to analog audio, and amplify it to properly driver the drivers.
Let’s have a look at a couple of Bluetooth headphones with built-in digital-to-analog converters.
The Tozo T10 earphones (link to check the price on Amazon) are a pair of true wireless Bluetooth earphones with built-in DACs and amps to convert the wirelessly-transmitted digital audio to analog audio.
The Bose QuietComfort 35 Series II (link to compare prices on Amazon and B&H Photo/Video) are Bluetooth wireless headphones with a built-in DAC, amplifier and active noise-cancelling circtuits for each driver.
Is sound analog or digital? Sound is made of mechanical wave energy that propogates through a physical medium. It causes localized pressure differences in the medium as it pass through. This is a considered to be analog since it is represented by a continuously variable physical quantity.
Why is digital audio preferred over analog? Digital audio has several advantages over analog audio including:
- Non-destructive editing
- Total recall of session set up (digital mixing consoles, digital audio workstations, etc.)
- Easily stored & highly portable
- Easily integrated into multimedia
- Exact multiple copies and replication for sharing
- Used for streaming
However, sound waves and sound/audio transducer devices (headphones, microphones and loudspeakers) function with analog audio. Therefore, DACs (digital-to-analog converters) are required to actually hear the information stored in a digital audio signal.