Since the first commercial digital recordings were released in 1971, eager listeners have been listening to digital audio through their speakers. Today, nearly all the audio we listen to through our speakers is digital (even with the resurgence of analog audio vinyl records).
Are speakers analog or digital devices? Though speakers are regularly connected to digital audio devices, they are inherently analog transducers. Speaker transducers convert analog audio signals (electrical energy) into sound waves (mechanical wave energy). Digital audio must be turned into analog audio in order to drive a speaker.
In this article, we’ll discuss the inherently analog nature of speakers; explain the differences between analog and digital audio, and touch on the role and functionality of digital-to-analog converters (DACs).
Analog Vs. Digital Audio
If we are to fully understand the analog nature of speakers, we must start by discussing the differences between analog and digital audio.
To begin with, audio (whether analog or digital) is a representation of sound that can be physically stored and played back, and be broadcast further than sound would be able to travel naturally.
Let’s define sound.
Sound is made of mechanical wave energy. The human range of hearing is between 20 Hz – 20,000 Hz and is often what we define as “sound.” This means we hear sound waves that oscillate between 20 and 20,000 times per second.
Infrasound happens below 20 Hz and ultrasound happens above 20,000 Hz.
These mechanical sound waves cause localized pressure variation in a medium (typically air in the case of speakers).
The waves are continuously variable quantities and are, by definition, analog. The term “analog” is defined as the measurements and representations of continuously variable physical quantities.
Let’s define analog audio.
We’ve defined the terms “analog” and “audio.” Analog audio, then, is a representation of sound waves (varying pressure) in the form of continuously variable electrical energy (voltage) waveforms.
The frequencies of the analog audio AC voltages, like the frequencies of audible sound waves, range from 20 Hz to 20,000 Hz.
To show the similarities between sound waves and analog audio waveforms, we’ll have a look at a visual representation of a 1 kHz (1,000 Hz) sine wave defined in both audio and sound units.
A 1 kHz sine wave completes one cycle or oscillation every millisecond.
Let’s begin by looking at the diagram of a 1 kHz sound wave:
The amplitude of the sound wave is measured as the pressure deviation from the ambient pressure of the medium. Units of pressure deviation are often decibels sound pressure level (dB SPL) but can also be in Pascals (Pa) or pounds per square inch (psi).
Note that the dotted “zero line” refers to the ambient pressure level of the medium. The wave goes to phases of increased pressure and decreased pressure. There is a peak of maximum pressure (max. compression) and a trough of minimum pressure (max. rarefaction).
Let’s now have a look at a 1 kHz sine wave as an analog audio signal and check for the similarities:
This audio signal waveform is meant to represent a sound wave. We can see that look the same.
The difference is that the amplitude of the analog audio signal is measured as an electrical voltage (potential difference). The units used to define the amplitude are either volts/millivolts or decibels relative to a voltage (dBV is relative to 1 volt while dBu is relative to 0.775 volts).
Just like the sound wave it represents, the analog audio signal has a peak and trough in each of its cycles.
Analog audio signals are alternating currents. The peak voltage represents the maximum positive voltage and forward-flowing current. The trough represents the maximum negative voltage and backward-flowing current.
The dotted centre line represents zero voltage and is the point at which current switches direction.
All this to say 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 define digital audio.
Digital audio can be thought of a digital representation of analog audio. So, then, it is a representation of a representation of sound!
Digital audio is not continuously variable. Rather, it is made of many audio samples per second that each have their own amplitude.
The samples and amplitudes have such high resolution that they approximate sound with incredible precision. However, they are still made of digital samples.
I almost wrote that digital audio has such high resolution that we hear it as we would analog audio. However, this would be false since we cannot truly hear digital audio. This is because any transducer, including speakers and headphones, requires analog audio to produce sound.
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 ultimately has discrete values.
Digital audio has numerous advantaged over analog audio but it cannot be used to drive speaker drivers/transducers!
The Speaker Driver/Transducer
The speaker driver(s) is the most important element in loudspeaker and monitor design. It is the transducer component responsible for converting audio signals (electrical energy) into sound waves (mechanical wave energy).
In order for the speaker drivers to work properly, the analog audio signal must be able to pass through a conductive part of their design. Typically this conductor is the voice coil (though there are other types of speaker transducers that do not rely on a voice coil).
The alternating current of the audio signal causes the speaker cone/diaphragm to oscillate back and forth and produce sound waves that mimic the waveform of the audio.
Digital audio is not a continuous alternating current and will not drive a speaker driver.
To learn more about speaker transducers, check out my article How Do Speakers & Headphones Work As Transducers?
Digital-To-Analog Converters (DACs)
Wait. If digital audio cannot drive speakers, how can speakers connect to digital audio devices and effectively produce sound?
For any speaker transducer to work with a digital audio device, a digital-to-analog converter (DAC) must be put in-line between the audio device and the speaker.
As their name suggests, DACs are devices that effectively convert the digital audio signal of the digital device into an analog signal that can properly drive the speaker(s).
DACs can be found in the following:
- Headphone jacks of digital audio devices (CD players, mp3 players, laptops, smartphones, tablets, etc.)
- Standalone adapters
- Power amplifiers and active speakers
- Audio interfaces
- Digital mixing consoles
For more information on speakers and how they relate to computers, check out my article Are Speakers (& Studio Monitors) Input Or Output Devices?
Let’s briefly discuss each of the common digital-to-analog converters used to connect digital audio sources to speakers.
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 speaker models.
Although these jacks are typically designed to drive headphones, some speakers can be effectively driven by the output signals of a headphone jack.
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 digital amplifiers 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. Its jack is sized at 3.5mm.
DACs In Amplifiers & Active Speakers
Speakers need amplifiers to boost the amplitude of the analog signal to a level that can properly driver the speaker drivers.
Many speaker amplifiers have digital audio inputs. Their built-in DACs turn the digital audio signals into analog signals before amplification.
This is true of both active speakers (which have internal amplifiers) and passive speakers (which do not have internal amplifier and, therefore, require standalone externals amps).
Let’s have a look at examples of a DAC in a standalone speaker amplifier followed by an active speaker.
The Denon PMA-60 (link to compare prices on Amazon and other online retailers) is a digital-integrated stereo amplifier. Its DAC utilizes Advanced AL32 digital audio processing to playback PCM files up to 384 kHz/32-bit, with enhanced dynamic range and improved resolution at low level.
Its digital inputs include:
- 1x USB-B (2-channel DSD and Linear PCM capabilities)
- 2x Optical (2-channel Linear PCM)
- 1x Coaxial (2-channel Linear PCM)
The Neumann KH 120 D (link to compare prices on Amazon and other online retailers) is a powered studio monitor with a built-in DAC. It has a BNC AES/EBU digital input and even has a BNC AES/EBU digital output. Its maximum sample rate and bit-depth of 192 kHz and 24-bit, respectively.
This is also the case in Bluetooth speakers. The Bluetooth protocol send digital audio wirelessly and so the BT speaker must have a DAC to convert the audio into analog audio before amplifying it to drive the speaker itself.
The JBL Charge 4 (link to compare prices on Amazon and other online retailers) is an excellent example of a portable Bluetooth speaker.
DACs In Audio Interfaces
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, speakers and other inherently analog audio devices to connect to computers. Audio interfaces work to connect input and output devices to computers.
To learn more about audio interfaces, check out the following My New Microphone articles:
• What Are Audio Interfaces & Why Would A Microphone Need One?
• How To Connect A Microphone To A Computer (A Detailed Guide)
• Best Microphone Audio Interfaces
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 left and right line outputs for monitor/speaker connectivity.
Note that the outputs of the 2i2 are not amplified. In order to properly drive the speakers/monitors, an amplifier must be present (either in-line or built-into an active speaker/monitor).
Digital Mixing Console DACs
Mixing consoles and recording devices tend to have outputs that can connect to speakers. Digital mixing consoles are no different.
However, because digital mixing consoles deal with digital audio, any outputs must have a digital-to-analog converter.
Powered mixers will amplifier the audio signal before it is sent to the speaker.
Passive mixers will output audio signals that require amplification before they can properly drive a speaker.
Is sound analog or digital? Sound is made of mechanical wave energy that propagates through a physical medium. It causes localized pressure differences in the medium as it passes through. This is considered to be analog since it is represented by a continuously variable physical quantity (pressure).
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