High resolution audio: myths and facts

The quality of sound is based on it’s high resolution audio. High-resolution sound is all the rage. Many of the manufacturers of stereo equipment, and more and more record labels, especially those that sell through the Internet, seem determined to convince us that high-resolution audio is what all of us who love music should aspire to if we want to enjoy it with the highest possible quality.

On paper, there are technical foundations that justify the existence of high-resolution audio and indicate that its quality should be higher than that offered by the CD. But there are also strong reasons that invite us not to take its superiority for granted, at least not so clearly, and to question some of the virtues that the industry sells us. Let’s see what high-resolution sound is, what we need to enjoy it, and, above all, if it really offers us a better experience than music with standard quality (that of the CD).

What is high resolution sound?

To understand in a simple way what high resolution sound offers us, it is good for us to review how music is stored on CDs that we all know. These records, unlike vinyl, allow us to store information in the digital domain, whereas vinyl records are analog. This means that the music on a CD is encoded in the form of ones and zeros, in exactly the same way as the information we have on our computer’s hard drive, which is also digital.

But a CD does not have an infinite capacity; in fact, the size of the tiny notches that we see on its surface if we look at it with a microscope and the distance that separates each of them from the adjacent ones reveals how much information it is capable of holding. Precisely, in a simplified way, this is what differentiates CD, DVD and Blu-ray Disc: the size of the small holes that encode the information and the distance that separates them. If we compare two discs with the same diameter, the one with these smaller and closer notches will have more capacity. This parameter, precisely, is what determines the wavelength of the laser that we must use to extract the information.

The technology of the CD format was developed in the late 1970s by Philips and Sony, and it was the engineers of the latter company who proposed to encode the information using a 16-bit resolution and a sampling frequency of 44.1 kHz. But these figures were not chosen at random; These specifications allow this format to reproduce sounds found in the frequency range from 20 Hz to 20 kHz, which coincides quite precisely with the frequency limit that the human auditory system is capable of perceiving, even bearing in mind that not all people have the same hearing ability.

The CD uses 44.1 kHz sampling to, according to the Nyquist-Shannon theorem, be able to reproduce frequencies up to 20 kHz

To understand what the resolution and sampling frequency is without going into too cumbersome details, we can think that in order to store an analog signal, and therefore continuous, in a digital medium, which has a limited capacity, it is essential « chopping ‘that continuous signal into small fragments, or samples, and inserting as many as will fit on the digital medium. Resolution tells us the number of bits that we can use to describe each of these samples, which, in turn, reveals the number of variations or possibilities that each of them can take. And the sampling frequency tells us how many we will be able to take.

If we stick to the characteristics of the CD we can see that our music is obtained by taking 44,100 samples per second (corresponding to 44.1 kHz) from the original analog signal, and each of them is encoded in a data packet that uses 16 bits. And at this point, finally, is where Hi-Res Audio comes into play.

The starting point of this technology is easy to understand: it assumes that if we increase the resolution, the sampling frequency, or even both parameters at the same time when passing an analog signal to the digital domain, we will be able to “reconstruct” the original analog signal. With more precision. And it really is. For this reason, the specifications commonly used in high-resolution audio formats are 24-bit 96 kHz, or 24-bit 192 kHz. Both options, on paper, should allow us to recreate the original continuous signal with more precision than the 16 bits and 44.1 kHz of the CD, or, what is the same, they will discard less information from the original sound take.

But this is not all. In addition, by raising the resolution to 24 bits, the dynamic range is increased and the signal / noise ratio improves. A 16-bit resolution allows us to encode a total of 65,536 possible levels for each of our samples, while a 24-bit resolution reaches 16,777,216 levels.

The resolution commonly used in high-definition audio formats is 24-bit, and the sampling frequency is 96 kHz or 192 kHz.

The difference between the two extremes, which is where the lowest and highest levels meet, indicates the difference in dynamic range between one resolution and another. With all this data on the table we can think that high resolution sound should offer us more quality than the audio of a standard CD. And it is so, but, as we will see later, there are factors that limit the experience and that users must take into account, beyond what the industry “sells” us.

The Internet: Key to HD Audio Success

At this point we can easily understand that the size of a sound file depends on the resolution and sample rate used to encode the music it contains. The same topic occupies much more if we digitize it at 24 bits and 96 kHz than if we digitize it at 16 bits and 44.1 kHz. However, we have a very interesting resource that helps us save space: compression. Hi-Res Audio is currently distributed in six different formats (some of them offer lossless compression): FLAC (lossless compression), ALAC (Apple’s proposed lossless compression technology), AIFF (is the Mac sound file), WAV (is the sound file format created by Microsoft and IBM for PCs), DSD DFF (SACD format encoding technology), and DSD DSF (a variant of DSD for Sony VAIO computers).

Of all the formats that I have just mentioned, the most used to distribute high-resolution music on the Internet are FLAC and ALAC because both offer a very interesting compression rate, and without loss of quality. And we all know that size matters on the Internet. And a lot. In fact, the network is playing an essential role in popularizing high-resolution sound.

The evident decline of physical media is causing many audiophile record labels to place a good part of their discography on the Internet in one of the two formats I have mentioned. Or even in both simultaneously so that we choose the one we prefer. It is common to find the same album in MP3 320 Kbps, with CD quality (16 bits and 44.1 kHz), at 24 bits and 96 kHz, and at 24 bits and 192 kHz. These last two formats are known as study masters. The price depends, of course, on the quality, being the MP3 the cheapest and the study masters the most expensive.

FLAC and ALAC formats are becoming popular because they offer a high compression rate without loss of quality.

As we told you at the time, Blu-ray Disc is a physical format suitable for distributing music in high resolution due to its large capacity. Indeed, Blu-ray Pure Audio, which contains only studio master-quality audio (the only images are the user menus), are trying to make their way onto the market, but they have it difficult given the unstoppable advancement of music distribution. via Internet. Some record labels that sell high-resolution music worth keeping track of are Linn RecordsHD Tracks2LProMates, and HD-Klassik, among many others.

This is what we need to take advantage of it

High resolution audio recorder

To be able to listen to music in high resolution audio, we simply need a device that incorporates a DAC capable of processing audio in the formats we want to reproduce, such as DSD, 24-bit / 96 kHz or 24-bit / 192 kHz files. The DAC incorporates the circuits responsible for the critical conversion of data from the digital to the analog domain, and therefore must be able to “understand” the information stream that it is going to receive. Otherwise it will be unable to decode it.

The range of consumer devices prepared to carry out this task is growing. Currently we can easily find A / V receivers, portable music players, smartphones, Blu-ray Disc players and other devices capable of processing files with studio master quality. What happens is that the experience that they are going to offer us is conditioned by the rest of the elements of our music equipment, and, of course, by our own auditory system.

If what we want is to listen to our music in high resolution audio on a portable player, such as a Sony Walkman or an Astell & Kern device, for example, we will only need to get some good headphones. And ready. But to enjoy these formats in a home stereo, in addition to the components that we all know (compact chain, amplifier, speakers, etc.) we will need a computer, a NAS or a network music player that is capable of storing the music. audio files and send them to the device that incorporates the DAC. The most common is that this communication is established through a USB link ( if it is asynchronous much better because this will reduce the jitter ).

One last note: fortunately we have a wide range of applications, both for Windows and OS X, that we can use to reproduce our files with studio master quality. Some of the most interesting are Audirvana, JRiver, FooBar, Amarra, Fidelia, BitPerfect and Pure Music, but there are many more. Ideally, you should try several and keep the one you like the most.

Plus? Yes better? With many nuances

If we stick to the specifications it is quite evident that high resolution music should offer us a sound quality superior to standard audio (considering CD quality as “standard”). As we have seen, a digital signal encoded with a 192 kHz sample rate and 24-bit resolution looks more like the original analog signal than a 44.1 kHz 16-bit digital signal. In addition, it is also superior in parameters such as dynamic range and signal-to-noise ratio. However, there are limitations that in practice will inevitably undermine our experience, and that, therefore, we must take into account. And the most overwhelming of all of them is the capacity of our auditory system.

According to experts, the human ear, in the best of cases, is capable of perceiving sounds whose frequency ranges between 20 Hz and 20 kHz. Anything outside of this range will go completely unnoticed by us. In addition, our hearing capacity deteriorates with age, especially the perception of high frequencies, so it is not surprising that many adults are not able to hear sounds that exceed the 14 or 15 kHz threshold. Something similar happens with the dynamic range: it is not clear that the jump from 16 to 24 bits provides a clearly appreciable improvement in “blind” listening.

High resolution audio

Another important limitation that we must take into account is that imposed by our own reproduction equipment. What is the use of having our music encoded in a format capable of reproducing frequencies of up to 48 kHz, as happens with files encoded with a sampling frequency of 96 kHz, if our speakers are not capable of exceeding 22 kHz? Some very high-end cabinets equipped with ribbon or silk dome tweeters exceed this figure, but most home speakers clearly fall short. In any case, this is just one example with which I intend to illustrate how difficult it is for the performance of a stereo to be in line with what files with study master quality offer us.

In a “blind” listening it is not at all clear that someone will be able to distinguish a CD from a 24-bit 96 or 192 kHz studio master quality file.

For all that I have discussed, in my opinion, high resolution music is interesting, but it is by no means a “universal panacea”. The theory argues that it offers us better sound quality, but it is clearly marginalized by the limitations I have just described. Very high-end equipment in the hands of a young person with a fine, healthy ear may be able to offer some very subtle differences between a CD and a 24-bit 96 or 192 kHz file. But, if they can be appreciated, they are surely marginal. I have done this test hundreds of times over the last few years, using “powerful” equipment, and I have come to a conclusion that I would like to share with you: the sound output is most important, not the bits and kilohertz.

A truly inspired recording will likely sound great on a 24-bit 192kHz studio master-quality CD, vinyl record, and file. And a sound shot that can be improved will leave much to be desired in any of these formats. For this reason, my recommendation is that, in addition to assessing the artistic quality of a work, which is essential, you make sure that its sound capture and mastering are really up to scratch. I would give even more importance to these parameters than to the format.

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