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24/192 digital audio format and why it doesn’t make sense. Part 3

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24/192 digital audio format and why it doesn’t make sense. Part 3

192 kHz is considered harmful

192 kHz digital music files offer no benefit, but still have some impact. In practice, it turns out that its playback quality is slightly worse, and ultrasonic waves appear during playback.

Both audio converters and power amplifiers are susceptible to distortion, and distortion tends to build up quickly in the high and low frequencies. If the same speaker reproduces the ultrasound along with the frequencies of the audible range, any non-linear characteristics will change part of the ultrasonic range to the audible spectrum in the form of uncontrolled random non-linear distortions that cover the entire range of audible audio. Non-linearity in a power amplifier will have the same effect. These effects are difficult to notice, but testing has confirmed that both types of distortion can be heard.

The graph above shows the distortion resulting from intermodulation of 30 kHz and 33 kHz audio in a theoretical amplifier with a constant harmonic distortion (THD) of approximately 0.09%. Distortion is visible across the spectrum, even at the lowest frequencies.

Inaudible ultrasonic waves contribute to intermodulation distortion in the audible range (light blue area). Systems that are not designed to reproduce ultrasound often have higher levels of distortion, around 20 kHz, which further contributes to intermodulation. Expanding the frequency range to include ultrasound requires compromises that reduce noise and distortion activity within the audible spectrum, but in any case, unnecessary reproduction of the ultrasonic component will degrade reproduction quality.

There are several ways to avoid additional distortion:

An ultrasound-only speaker, amplifier, and signal spectrum splitter to independently separate and reproduce ultrasound you can’t hear so it doesn’t affect other sounds.
Amplifiers and transducers designed to reproduce a wider spectrum of frequencies so that ultrasound does not cause audible harmonic distortion. Due to the additional cost and complexity of the performance, the additional frequency range will reduce the quality of reproduction in the audible spectrum.
Well-designed speakers and amplifiers that do not reproduce any ultrasound.
For starters, you don’t need to encode such a wide frequency range. You cannot (and should not) hear ultrasonic harmonic distortion in the audible frequency band if there is no ultrasonic component.
All of these methods are meant to solve a problem, but only 4 ways make sense.

If you are interested in the capabilities of your own system, the following samples contain: 30 kHz and 33 kHz audio in WAV 24/96 format, a longer FLAC version, some melodies, and a cut of normal songs at 24 kHz to make them drop fully in the ultrasonic range of 24 kHz to 46 kHz.

Tests to measure harmonic distortion:

30 kHz audio + 33 kHz audio (24 bit / 96 kHz) [5 second WAV] [30 second FLAC]
Tunes 26 kHz – 48 kHz (24 bit / 96 kHz) [10 second WAV]
Tunes 26 kHz – 96 kHz (24 bit / 192 kHz) [10 second WAV]
Cutting songs down to 24 kHz (24-bit / 96 kHz WAV) [10-second WAV] (original cut version) (16-bit / 44.1 kHz WAV)
Suppose your system is capable of playing all formats with sample rates of 96 kHz [6]. When playing the files above, you shouldn’t hear anything, no noise, hiss, clicks, or other sounds. If you hear something, then your system has a non-linear response and causes audible non-linear distortion of the ultrasound. Be careful when turning up the volume, if you enter the digital or analog clipping area, even a soft clipping can cause strong intermodulation noise.

In general, it is not a fact that harmonic distortion of ultrasound is audible in a particular system. The distortion introduced can be negligible and quite noticeable. In any case, the ultrasonic component is never a merit, and in many audio systems it will lead to a sharp decrease in the quality of sound reproduction. In systems where it does not damage, the ability to process ultrasound can be preserved or instead, resources can be used to improve the sound quality of the audible range.

Misunderstand the sampling process

Sampling theory is often incomprehensible without the context of signal processing. And it’s no wonder that most people, even brilliant doctors in other fields, don’t get it. It’s also not surprising that many people don’t even realize that they are making a mistake.

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24/192 digital audio format and why it doesn’t make sense. Part 2

24/192 digital audio format and why it doesn’t make sense. Part 2

Perfect hearing or hereditary gift

When I receive many letters, I see that many people believe in the existence of unique people with exceptional hearing. Are there really such people with “golden ears”?

It depends on what you call exceptional hearing.

The healthy ears of young people hear better than the ears of the elderly or damaged ears. Some people are exceptionally well trained to hear all the nuances of sound and music that most people don’t even know exist. In the 90’s, it could recognize all mp3 encoders (they were all pretty bad at the time) and it could prove it in a double-blind test [2].

If a person has healthy ears and is well trained to recognize sounds, I would say that their hearing is exceptional. However, people with below average hearing may be able to notice details that elude inexperienced listeners. Exceptional hearing is largely a matter of training, not the ability to hear beyond the hearing range of ordinary mortals.

Hearing researchers would love to find someone with exceptional hearing and the ability to hear outside the auditory range to test and record the research results. I have nothing against ordinary people, but every scientist wants to find a person with genetic peculiarities to write a first-class article. We haven’t found such people in 100 years of testing, so they probably don’t exist. So sorry. But we will continue to search for more.

Love for the color spectrum

You may be skeptical about everything I just wrote because it goes against all marketing tactics. Instead, suppose people have a craze for color and deviate from the subject of sound.

The figure above shows a rough scale of the sensitivity of rods and cones in the human eye, compared to the visible spectrum. These senses respond to light in overlapping spectral bands, just as the hair cells in the ears are tuned to perceive overlapping sound frequency bands.

The human eye sees a limited range of light waves called visible radiation. Here is a direct analogy with the audibility range of sound waves. Like the ear, the eye has sensitive cells (rods and cones) that capture light in different but overlapping frequency bands.

Visible radiation begins at a frequency of approximately 400 THz (dark red) and extends to 850 THz (dark purple) [3], but visual acuity decreases with the course of life. Outside of this approximate range, the intensity of light entering your eyes can burn your retina. So it turns out that the range is quite decent even for young, healthy and genetically gifted individuals, a range that is analogous to a wide range of the audio spectrum.

Suppose in our hypothetical world, where there is a craze to expand the visible spectrum of video recordings, there is a group of people who believe that these restrictions are not generous enough. They believe that video is not only the visual spectrum, but also infrared and ultraviolet radiation. Continuing with the comparison, let’s assume that the most active part of the group (who is proud of it!) Also claims that this spread spectrum is not enough, and the video will appear more natural if microwaves and X-rays are reached there. For those who have an “eye is a diamond”, the difference will be enormous, just day and night!

Of course, this is ridiculous.

No one can see X-rays (not infrared, not ultraviolet, not microwave). No matter how strongly a person believes in what they can, the retina simply does not have the tools to perceive them.

Here’s an experiment anyone can do: Go and grab the Apple IR Remote [TV]. The LED emits a wavelength of 980 nm, roughly equal to a frequency of 306 THz, which is close to the infrared spectrum. Waves of this length are not that far out of the visible range. Take the remote control to the basement or darkest room with the lights off in your house in the middle of the night and let your eyes get used to the dark.

The image above is an Apple TV infrared remote control, captured with a digital camera. Although the emitter is bright enough and the frequency of the radiation is close to the frequency of the red part of the visible spectrum, infrared radiation is completely invisible to the human eye.

Can you see how the remote control’s LED lights up when you press the [4] button? No? Even a little peek? Try some other remotes, many of them use infrared in the 310-350 THz range.

24/192 digital audio format and why it doesn’t make sense. Part 1

24/192 digital audio format and why it doesn’t make sense. Part 1

Unfortunately, there is no point in recording music 24/192. Its fidelity does not dramatically exceed 16/44 or 16/48 formats, but it takes up 6 times more space.
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Earlier headlines reported that musician Neil Young and Apple founder Steve Jobs were discussing a possible launch of a service to download “uncompromising studio quality” music formats. Most of the newspapers, magazines and users were quite optimistic about the prospects of a digital music format with signal quantization in 24 bits, at a sampling frequency of 192 kHz.

Unfortunately, there is no point in recording music 24/192. Its fidelity does not dramatically exceed 16/44 or 16/48 formats, but it takes up 6 times more space.

Today, there are several problems associated with audio quality and the “application” of digital music distribution. The 24/192 format does not resolve any of them. As long as everyone regards this format as a panacea, we will not see any improvement in the field of music.

Let’s start with the bad news

Over the past few weeks, I have talked to smart, scientific people who believe in the 24/192 music format and don’t understand how anyone can disagree with it. They asked good questions that are worth answering in detail.

I also wondered what could be causing such active support for high sample rate digital audio. The responses showed that few people understand the basics of signal theory or the sampling theorem (the Kotelnikov or Nyquist-Shannon theorem), which is not surprising. Misunderstandings about mathematics, technology and physiology were evident in the speeches of many professionals with extensive experience in audio technology. Some have even argued that Kotelnikov’s theorem does not explain how digital audio works [1].

Disinformation and prejudice only play in the hands of charlatans. Let’s go through the basics of why the 24/192 format doesn’t make sense before presenting other more valid ideas.

Gentlemen, welcome! Your ears!

The ear listens with the help of hair cells, which are located on the resonant basilar membrane in the cochlea of the inner ear. Each hair cell is precisely tuned to a specific narrow frequency range, which is determined by the position of the cell on the membrane. The peak of the sensitivity is in the middle of the frequency range, which gradually decreases in both directions and takes an asymmetrical cone-shaped shape, overlapping the frequency ranges of neighboring cells. We do not hear sound if there are no hair cells tuned to that frequency.

The left side of the figure shows a cross section of a human snail with a basilar membrane (beige in color). The membrane is designed to resonate in different places along its length, depending on the incoming frequency: high frequencies resonate closer to the base and low frequencies at the opposite end. The figure shows the approximate locations of various frequencies.

The right side is a schematic diagram of the response of hair cells along the basilar membrane, as a group of overlapping signals.

The process is similar to an analog radio receiver, which receives the frequency signal to which it is tuned from a nearby radio station. The more the receiver and station frequencies do not match, the more unstable and distorted the signal will be, regardless of its strength. There are upper (and lower) levels of the frequency range beyond which hair cells cannot receive signals and we cannot hear anything.

Sample rate and audible frequency spectrum

I’m sure you’ve heard many times that frequencies 20 Hz to 20 kHz are the audible range of the human ear. It is very important to understand how scientists obtained such numbers.

First, we measure the “hearing threshold” across the entire audio range for a group of listeners. This allows us to construct a curve that represents the quietest sound the human ear can hear at any given frequency, measured under ideal conditions in healthy ears. An anechoic environment, accurate calibration of breeding equipment, and rigorous statistical analysis are an easy part of the experiment. Auditory concentration is lost very quickly, so the test must be performed while the subject is not tired. As a result, there are many breaks and pauses, and testing can take from several hours to several days, depending on the methodology.

24 bit depth?

How come people start hearing higher quality with some kind of 24 bit DAC instead of the usual 16 bit?

The answer to this question, like the answer to many other questions, lies in the workings of the human brain. You can easily realize that, in fact, music exists only in our head and consciousness already receives it in a processed form from the subconscious. The subconscious mind, in turn, has an incredible effect on how we see things (literally). And everything that passes through the senses passes through the subconscious without fail.

So the wine for $ 10 seems tastier than the wine for $ 1, although in fact, both there and there the same body is poured. We fully understand that price does not mean high quality, but when we don’t think about it, the brain can very easily fill in the picture in the way it thinks best. And the subconscious mind is capable of operating with very complex structures, much more complex than the price of the product. Marketers know this very well. An old way to sell a pig in a poke, like an expensive DAC, is to compare it to a conventional audio system, but in the case of an expensive DAC, also increase the volume of the audio recording by 0.2 decibels. People do not consciously feel the difference, but the subconscious senses it. At the same time, it’s been known for a long time that people like louder music better. This is how an expensive DAC starts to sound “better” than usual.

The same goes for other components. So people believe that the sound has improved by replacing the USB cable. Or they think that tube sound is better than electronic. In fact, tube amps sound different than electronic ones, but that doesn’t mean that one is better or worse than the other. But without thinking, many, recognizing the “warm tube sound”, immediately prefer it to any other, although it can be emulated in electronic components with equal success.

And to me, in principle, I do not care, but I let them not dirty other people’s brains with these opinions. Better to let them honestly say they like this type of sound and stop saying it’s better.

The most surprising thing to me is that there are even people among audiophiles who pathologically hate digital sound. When digital sound first appeared, everyone from audio engineers to musicians was delighted with its quality. Before its introduction, all analog media were loud and wore out over time. It was impossible to listen to your favorite composition without the crackle or background noise, typical of vinyl records of that time, which was heard many times.

Digital sound on audio discs was perceived as something from another world: for the first time, music could be heard in perfect quality, without any external noise. And this recording could never deteriorate over time and could be transferred to other people via electronic means of communication without loss of quality.

But an extremely low percentage of people perceived this new digital sound with manifest horror. Digital sound sounded so unusual to them, used to analog recordings, that it seemed to them that the melodies with which they were familiar had lost their depth and familiar atmosphere. Just as some people long ago believed that photographs took people’s souls away, early audiophiles believed that digital recording took people’s souls away from music.

This trend continues to this day, although few have seen it in such extreme form. But its main meaning remains, the soul of the music needs to be returned. It doesn’t fit in 16 bits and 44.1 kilohertz, it needs 24 bits and 192 kilohertz. Some also need ritual items like gold wires or server-sized DACs. Some people use ultra-precise watches (oscillators) worth several thousand dollars, which they could not find useful in any professional study. Others diligently determine the processor load during music playback, believing that this affects the quality (in fact, the only thing the processor needs to do is take time to decode the music stream into an uncompressed format and poison it in the DAC before de as it ran out of data to convert and all modern processors cope with this without a problem). The list goes on and on, it would suffice for a series of articles.

Naturally, dozens, if not hundreds, of companies whose activities border on actual fraud benefit from all this. Ordinary people suffer from this too, sometimes spending several thousand dollars on a DAC that has no meaning to them instead of buying high-quality speakers for the same money.

Sample rate and bit depth

The comparison with the digital or film camera is not completely random: the sampling frequency of the audio signals, that is, the frequency of the samples per unit of time (usually given per second), is comparable to the frame rate per second from a film camera. The number of pixels in each individual image could be equated with the bit depth: HD movies “look better” than Super 8 movies. The higher the number of pixels on the sensor and the more often a photo is taken, more precisely, the “light to be recorded”, the landscape, can be digitally reproduced.

Bit Depth

Bit depth

Fortunately for us, a certain Harry Nyquist inspired a certain Claude Shannon long ago to support him with a theorem (a theoretical statement or theorem) that stated that an audio signal at twice the frequency must be sampled uniformly to match. with the original signal. to be able to rebuild sufficiently. Limiting the bandwidth of audible frequencies practically frees us from our hearing, which is basically only capable of consciously perceiving frequencies between a maximum of 20 Hz and 20,000 Hz.

Sample rate

The expense of completely and exactly reconstructing the analog output signal is theoretically infinite, since digital signals are discontinuous by nature in any case, while analog signals are always continuous. Unfortunately, it is inevitable that digital information is only suitable for rough storage of analog signals. The starting signal is “rough”, good word, right? Nyquist’s theorem also applies to digital cameras: they also deal with frequencies, that is, those of light.

digital audio

For signals up to 20 kHz more or less relevant to humans, a sampling frequency of 40 kHz is sufficient according to the aforementioned theorem. The 44.1 kHz sample rate common for CD quality comes from the 1970s or Sony’s “pulse code modulation (PCM) process for storing digital signals on video tapes. Later, Sony developed the Red Book standard for audio CDs with Philips.

The frequency, which is slightly wider by an additional 4000 Hz than twice that audible to humans, has its origin in the simplest possible filters, which are intended to remove so-called aliasing effects from the audible range of the reconstructed analog signal. during digitization: the wider this “corridor”, the simpler the filter technology.

PCM pulse code modulation method

Exactly 44.1 kHz got out of this, because sample rate converters can be more easily designed (used for studio technology or data carrier transfer) if the sample rate is an integer multiple of the output frequency. The output frequency here was the 60 Hz network frequency used for video digitization with 525 lines to digitize the TV signal. Changing 60 Hz would have been very laborious, it stuck. It is not a coincidence that multiplying 525 by an integer factor results in a frequency greater than 44,000 Hz, which we want to achieve to keep filters for anti-aliasing simple: the next largest integer that is divisible by 525 is 44,100. The multiplication factor is 84, as a whole number is desired, which should not interest us otherwise.

What is the audio bit depth?

Understand what bit depth is, how it works, and how this feature will affect the quality of music during auditions;

Currently, many of those who are looking for quality audio or quality music keep mentioning “Hi-Res”, FLAC 24-bit, and MQA (Master Quality Audio) files. This is a growing trend in high-end smartphones that are trying to offer higher audio quality both in their DAC and in support of advanced Bluetooth audio codecs like LDAC, developed by Sony. Additionally, there are music streaming services that promise lossless audio quality, like Tidal.

BitDepth

The promise made by audio equipment manufacturers, developers of audio streaming and music streaming formats, is simple: superior audio quality due to the increased amount of data, also known as bit depth or English bit depth . There are 24 bits of 1 and 0 versus 16 bits on the CD. Of course, these high-resolution files are more expensive due to their quality, but the more bits, the better the result will be when listening to music, right?

Bitdepth

Low resolution audio is usually displayed using a jagged wave graph (with ladders). Source: soundguys
Low resolution audio is usually displayed using a jagged wave graph (with ladders). Source: soundguys
Well, the answer to the previous question is: not necessarily. The argument for a value in increasing bit depth is not based on something scientific, but on the distortion of what is actually happening and the exploitation of consumer ignorance about the media they are consuming. That is, it is a fact that stores selling 24-bit tracks reap far more benefits than a real improvement in promised sound quality.

Bit depth and sound quality.

The greatest example of companies selling 24-bit audio is the demonstration of a jagged sine wave, like stairs. When we look at a file that has a resolution of 16 bits, we see an irregular line, but when we look at the same song in 24 bits, it seems to be a practically smooth line, with better definition. It is a basic visual illustration, but depending on the person’s knowledge of the subject, he can be easily fooled.

Why use 24-bit or more audio files?

The utility of using a high-level bit depth applies to studios, because with each filter and conversion that is applied, the background noise increases. This increase in noise occurs due to the insertion of a new wave, as explained above. In other words, when using a higher bit depth level, the sound engineer prevents the original audio from generating noise by manipulating it for mixing and mastering.

However, remember that this will be more useful for audio production and not for the listener, as explained above.

conclusion
What will make the difference will be the balance between the sounds made in the mastering and not the bit depth itself, since the 16 bits of the CD are already more than enough for music listeners.

Multimedia formats: Digital audio

Sound is a continuous signal. To be stored with computer systems
it must be sampled, thus obtaining a digital signal.
The parameters that characterize the sampling are basically three:

 The sample rate
 Bit depth
 The number of channels
these parameters influence both the space occupied and the quality of the audio file
digital obtained.

Digital Audio

Sampling rate

The sampling frequency is the measurement expressed in Hertz (Hz) of the number
of times per second in which an analog signal is measured and stored
in digital form.

The higher the sampling rate, the more the sequence of the samples
digital will be close to that of the original analog waveform.
Low sampling rates limit the frequency range that is
can record, which in turn can generate a recording that
poorly reproduces the original sound.
Two sampling frequencies:
A. Low sampling rate,
which distorts the wave of the original sound
B. High sampling rate,
which perfectly reproduces the wave of
original sound
To reproduce a certain frequency, the sampling frequency
it must be at least double it (Nyquist theorem).
For example, audio CDs have a sampling rate of 44.100 Hz,
so they can reproduce frequencies up to 22.050 Hz, which are hardly found
beyond the limit of human perception of 20,000 Hz.
The following table shows the most common sampling rates for
digital audio.

Bit depth

The bit depth represents the number of bits used to store a
single digital sample.
When a sound wave is sampled, each sample is assigned
the amplitude value closest to the original wave amplitude. A depth
in high bits it provides as many amplitude values as possible, which results in a
greater dynamic range (the difference in decibels between the maximum volume that the component can sustain without
distort the waves and the background noise it produces), lower and higher background noise
fidelity.
For example if you use 8 bits you have 256 possible values (28
) that, being
relatively few, offer less sound quality than a
tape; if instead 16 bits per sample are used, 65536 values are obtained
possible (216).
The most common examples are the audio CD, recorded in 16 bit, and the DVD, which
supports up to 24 bit depth.

Compression formats

Hand in hand with the advent of digitalization, multimedia applications have
they are increasingly widespread until they become commonplace. One of
multimedia features is certainly the use of digital audio
vowel and sound. The biggest obstacle associated with digitizing audio is
the large size of the files that are produced, which puts them at
sector operators (especially those linked to the internet) the problem of
reduce the space occupied by the data to obtain the double advantage of:
 save in terms of memory occupation;
 save in terms of transfer time on the network.

For this reason, speaking of digitizing the audio, it is necessary to speak
also of data compression techniques. The compression techniques of the
data, of whatever nature they are, are divided into:
 lossless: compress data through a lossless process
of information that takes advantage of redundancies in data encoding
 lossy: compress data through a lossy process
of information that takes advantage of redundancies in the use of data.

Lossless formats

Lossless compression formats are more suitable for archiving rather than
to reproduction, since most of them require complete
decompression before they can be played.
One of the most common lossless compression formats is FLAC (Free Lossless Audio Codec).

Lossy formats

Lossy compression formats use compression algorithms capable of
drastically reduce the amount of data required to store a sound,
guaranteeing however an acceptable and faithful reproduction of the original file uncompressed.