Analog vs Digital Audio [What is the difference? Read Guide 2019]

Many disputes, what is better analog or digital audio signal, can digital sound as good as analog, are continued despite digital devices successfully and rapidly replace analog ones. There is opinion, the main difference between digital and analog audio is analog closer to an original. It looks like, the analog waveform is smoother than "stairs" of digital music. On the other hand, a digital signal is not "stairs" actually. Not all is quite so simple. Read to end the easy and detailed explanation by audio software developer Yuri Korzunov.

What is analog and digital audio

• Analog audio is continuous audio signal (electrical, electromagnetic, mechanical, acoustic).
   
• Digital audio is the way to the presence of analog audio as number sequence. There are 2 types: Pulse Code Modulation (PCM) and Direct Stream Digital (DSD).

Analog and digital audio

We can see, that digital signal is a virtual math model of an analog signal in the digital domain. I.e., despite, the digital signal consists of separate samples, and the first wish is to connect lines in the "stairs", a discrete digital signal is continuous waveform math point of view.

If we ideally upsample digital signal to the infinite sample rate (interpolate/restore virtual samples between real samples), the digital waveform will be uninterrupted and equal to analog one.
The connection line is the same to steel ruler, that fixed in the points of real samples.

The same way is restoring a digital signal to analog form. There we get a continuous signal for any sample rate.
It happens, because the analog filter of a DAC is ideal interpolator, that smoothly and correctly connect digital samples.
We can see it in the picture above.

Sound quality

In the article, we'll consider what is better sound quality: digital or analog?

Sound quality has 2 definitions:

1. Level of distortions - the lower level is better audio quality;
2. Subjectively estimated sound quality.

Sound quality definitions

Both audio types have the same source - analog musical or another signal.

However, the next stage is storing and reconstruction to played back an analog signal. And the stage causes different losses for various audio systems. We can compare an analog vs digital system at this stage only.

Sound quality measurement

Definition #1 (distortion level) depends on the sensitivity, accuracy, and precision of a measurement tool.

Definition #2 (ear test) can be partially free from subjective biasing due to big numbers. Measurements are provided via blind tests. However, it is not a simple procedure.

Distortion-level sound quality and ear-test sound quality may be uncorrelated in some cases. It happens, because various patterns of the measured distortions may impact differently to ears and brain.

Look an infographic of analog vs digital audio quality comparison, where essential factors are shown.

Analog vs Digital Audio Comparison
(click for enlarge)

We can see, that before the original acoustical signal comes to medium, it pass through electro-mechanical (microphone) and electrical devices. To throw out factors, that common for all systems, below we'll consider original electrical signals directly before and after the mediums (tape, vinyl, digital unit) and its conversion devices (tape heads, vinyl recorder and player cartridge, including circuits, ADC, DAC).

Analog audio quality

Let's consider an analog audio system.

Mechanical issues

A vinyl recording is produced mechanical way (see simplified workflow):

1. Special stylus at a grooving machine cut grooves at a master disk according to an original electrical signal;
2. A nickel stamping record is produced from each side of the master;
3. At a pressing plant, vinyl LP disks are pressed to distribution.

In each of the stages, some mechanical deviations appear.

Production of vinyl disks is not ideal too

"Wow and flutter"

"Wow and flutter" effect is caused due to rotation speed deviation or magnetophone tape stretching.
The speed deviation alters the time of playback of the same tape or groove length. It causes frequency bias, that leads to total waveform distortions.

"Wow and flutter" effect. Waveform distortions

The speed deviation happens during recording and playback.

Temperature

Mechanical processes are sensitive to environmental temperature. As an example, it can cause an altering of play in bearings. The play may cause variations of "wow and flutter" effect.

Wear and tear

With wear and tear of the mechanical parts, audio parameter precision and accuracy degrade. It can cause increasing of distortions.

A tonearm angle altering

When a tonearm playback LP disk grooves at different distances from its center, angle of a stylus tip relative the groove is changed. It alters playback characteristics. The issue may be partially solved via tangential tonearm, that moves to the LP center with constant angle. But any mechanical device has parameter deviations, that impact to sound.

Tangential tonearm

Noise

The main issue of analog mediums is noise.

Vinyl disks are sensitive to dust. It causes temporary mechanical distortions of the disk surface. The disk cleaning is very desirable.

Vinyl and dust

A tape has noise due to magnet layer physical processes. There are some noise reduction systems. But it can't extremely reduce noise, like digital systems.

Tapes and vinyl records also wear and tear with storage and/or using time. Vinyl disks may be warped, scratched. Tapes may be stretched, well-worn and degaussed.

Analog noise

Electronic components

Electronic elements (transistors, tubes, others) of analog musical devices wear with time. Values of the element's parameters may come out of allowable range and lead to higher non-linear distortions and other.

Electronic components are a source of analog noise.

Degrading of electrical, magnetic, mechanical parameters also touch cartridges of LP players and tape heads.

Loudness limitations

In general, analog mediums put more loudness limitations for recorded audio stuff, than digital ones.

Overload and clipping

Output analog signal is limited by the maximal level. Close to the level, non-linearity is increased dramatically and output signal can't grow above the level despite the input signal is rising. So, the output waveform is distorted.

Analog overload and "soft" clipping

It's called "overload". And such output waveform distortion is called "clipping".

At the picture, we can see the smooth transient-clipping zone in point A. Such transient type leads to "soft" clipping of output waveform.

As rule, analog signal cause soft clipping - linearity is decreased smoothly.

Digital audio quality

Let's consider a digital audio system.

All its parts, that conduct or convert, from/to analog signal, cause phase, frequency, non-linear distortions.

Electronic elements of analog parts of the digital musical devices wear with time like the same items in analog systems.

Clock stability, jitter

Stability of the clock signal of ADC (analog-to-digital converter) and DAC (digital-to-analog converter) is very important. There are deviations:

• frequency;
• phase and front steepness (jitter).

The issue may be considered as similar to "wow and flutter". But, currently, digital-system clock stability is very high, comparing speed deviation of analog systems, in most cases.

Jitter in digital audio

Digital power amplifiers

Digital music systems may not be pure "digital". Because humans can receive analog acoustic waves only. But, in the author opinion, we have some trend to reduce the analog part share in audio systems.

D-class power amplifiers, based on sigma-delta modulation (like DSD), exists a long time. But they still not popular enough despite these amplifiers allow to get rid of digital-to-analog converters (DAC) and are fine compatible with the DSD.

Digital vs analog power amplifiers

Digital overload and clipping

If no additional processing, overload in digital format cause loud click due to positive value transformed to negative one momentarily.

Traditional digital overload and strong waveform damaging

Fixing of digital overload issue via compressor/limiter in the analog domain

To avoid digital overload, analog compressing and/or level limiting of an input signal of ADC (analog-to-digital converter) may be applied.

Special processing provides traditional clipping into the digital domain. The clipping may be:

• momentary or
• soft, like analog.

Momentary digital clipping (safe digital overload)

"Soft" digital clipping (analog overload emulation)

Overload may be avoided via analog compression of input analog-to-digital converter's signal.

When overload might occur into the digital domain, float point formats may solve the issues. The formats provide 0 dB level for 1.0.

If overload happens (1.1, as an example) it will not be clipped. At the final stage, the overloaded peak level may be normalized back to 0 dB.

How to avoid digital clipping in float point format

Digital vs analog sound quality

Digital versus analog audio systems

Analog vs digital audio outputs

What is most recommended: analog and digital audio outputs? Before answer the question let's consider the scheme.

Analog vs digital audio outputs

We can't see a significant difference between paths from the digital mediums to analog devices at upper (analog output of the digital device) and lower (digital output) parts of the drawing.

Factors impact to sound quality:

• Cable length and quality;
• DAC quality.

Connection via digital vs analog outputs

Analog connector types

In general case, no difference for sound quality between these connectors. However, a balanced connection may improve the signal-to-noise ratio. It may be important in hard electromagnetic interference environment and for long cables. A necessity in balanced connection is defined experimentally by ears or measurements at an audio device output.

Digital connection types

Meta-information is data about transmitted information.

Below we can see throughputs for different audio resolutions. It should be lesser than the maximal throughput of a digital connection with an accounting of the meta-information.

Throughputs of audio resolutions

Read more about audio interfaces

Analog versus digital mixing and gain control

Most popular audio editing are analog mixing and gain control. The mixing and gain control are implemented in analog circuits and components (transistor, tubes, operational amplifier, and others).

Digital audio is a form of analog audio coding. From a math point of view, no difference between analog and digital gain control. Look at the formula of gain control for both digital and analog audio:

output(t) = input(t) * gain,

where t is time.

At first glance, digital values are discrete and cause precision losses.

But, a digital signal is not "stairs". We should consider it as a continuous function with some bit depth, that causes a certain noise level.

Using float point math to gain control allows to apply gain and mixing transparently for audio stuff.

It is necessary to remember, if we multiply 16-bit integer values, the result should be placed to a 32-bit integer value and truncated back to 16 bit. After all processings, dither is recommended.

Result of multiplication of two 32-bit float values is 32-bit float value.

Analog gain control may be implemented in different ways. As an example, a switchable resistor kit can provide dB-scaled gain control.

1...2 dB-step implementation is significantly easier in float point formats, comparing 16/24-bit integer variables.

Using electronic components in gain control circuits cause non-linear distortions, noise, temperature instability.

But, for level adjusting of:

• analog devices in a pure analog system, or
• digital units, to avoid reducing of actually used bit depth (dynamic range),

analog gain control may be used.

Digital vs analog mixing and gain control

Analog vs digital audio production, recording proc and cons

Analog vs digital technologies in music and audio production, recording

Are speakers analog or digital?

In the general application, a speakesr are pure analog device. There are drivers with passive electrical components.

But some speakers contains amplifier(s) inside. Teoretically, it allow:

• achieving better adjusting the amplifier with driver(s),
• applying active (at active electronic components - op-amps, transistors) crossovers with higher abilities.

The amplifier may be digital.

The crossover may be implemented in the digital domain, that give more potential abilities, than crossover on the active components. But, DSD-input signal demands additional tricks for editing (EQ, gain contlrol). If the editing is done properly, it is almost transparent for the audio signal.

Analog versus Digital. Conclusions

1. Analog mediums have serious electromagnetic, electrical and mechanical, aging, environment issues that degrade stored and played back audio signals.
   Engineers try to reduce negative mechanical effects of analog devices in different ways. But, according to invention theory and practice, the best way to get rid of an issue is to get rid of the issue source. I.e. removing mechanical parts automatically remove their issues.
    
2. Digital systems have some degrading issues too. Primarily into analog parts or when digital audio is converted to/from analog signal (jitter, non-linearity, etc.).
   Lower bit depth and sample rate may cause sound quality degrading. But, even, minimalistic 16 bit / 44.1 kHz is good enough, the best analog sources. Of course, implementation as analog as digital units is matter.
    
3. In the digital domain, audio may be successfully restored after damaging, when special coding is used. Degraded analog stuff cannot be restored.
    
4. The workflow of digital music production and distribution is significantly easier, than analog mediums and provide lesser distortion level.
    
5. On the other hand, specific distortions of analog mediums (tape, vinyl, tubes) may have artistic character, that сan give an impression of better sound.

Read more:

How to play DSD | Player Software List | Read Quick Guide

DSF vs PCM. What is common base? [Article]

DSD High-Resolution Music Downloads [Check Free Files]

Audio Converter List | Read Comparison

DSD vs FLAC [Comparison, Infographic, Explanation]

PCM Audio [Quick Explanation. Myth Reasons]