Sound Quality

     in Audio Reproduction

There are numerous stages involved in audio reproduction, and achieving good end results requires quality at every stage. As listeners, we cannot influence the work done in studios and during recording. However, even here there are significant differences, and in real life, a common normal distribution applies – a lot of mediocrity and a touch of quality, along with some junk. Fortunately, we have the choice of what to listen to.

Audio reproduction begins today from digital sound files, composed of zeros and ones. And for the chain, we must also mention the endpoint: human hearing. According to widely accepted views, a person cannot distinguish more audio information than what a CD format can offer.

When discussing temporal information, two characteristics can be distinguished. One is how often we record the information, and the other is how much information is recorded at each respective moment. For CD-level audio, information is recorded 44,100 times per second, or at a frequency of 44.1 kHz. The other aspect, sentence length, is 16 bits. This means that when writing down an audio waveform, there are 65,536 possible levels. In simple terms, all instruments are sampled, and other factors are simply very frequently recorded points of audio waves, from which devices later reconstruct the audio waveform. These are distributed across the frequency range from the threshold of hearing to the point of hearing damage. Recording audio below or above this level is not practical; this range has a span of 96 dB. This also determines the distinction between the audio signal and the level of noise. Both older and newer blind tests confirm that beyond this level, listeners cannot discern an improvement in audio quality (this is also explained physiologically in terms of inner ear structure and function). Due to rapid advancements in digital data processing, today higher frequencies and sentence lengths are possible. Standards are already becoming 192 kHz 24 bits. And if the technology allows, this unfortunately may not stop there.

Having an audio file is not sufficient on its own. The audio file must reach the music-processing device. This is where the next term comes into play: the product of the two previous ones – the bit rate. For CD-level audio, 44,100 x 16, this equals 1,411,200 bits per second, or an audio transmission rate of 1.4 Mbps. Now, when compared to common transmission rates of 96, 160, 256, or 320 kbps offered by most music streaming services, their offerings seem rather feeble. However, here comes the role of music compression algorithms. The idea is simple: remove the part of music information that the listener wouldn't hear anyway, or that can be recalculated when unpacking. In any case, it is clear that the compressed information is not entirely equivalent to the original. Fortunately, real-life testing prevails here; if the compressed information were significantly worse, the format or service provider would quickly lose popularity. Allegedly, the impact of compression is audible, and in my unfair test, a spatial difference was discernible in a choral piece by Pärt.

Here, an real story fits in. I entered my bedroom in the evening, started playing music, and began reading news on my phone. About 10 minutes went by, and everything seemed fine. Gradually something seemed off with the sound. I continued reading the news, but now I also started listening. Eventually, I couldn't ignore it and went to check the speakers. I had accidentally left the wrong output selected. Behind it was a makeshift speaker cabinet with a single loudspeaker for testing...

So, in 99% of real-life cases, premium-level streaming and large MP3 files are entirely appropriate. And this is primarily due to the next stage: how streaming reaches the audio device. If it's through a digital or optical cable, it's lossless and can proceed. However, the prevalent next step nowadays is Bluetooth. Leaving aside lengthy discussions about compression and formats, the most robust transmission format is LDAC, with a maximum speed of 990 kbps. Achieving this requires spending time navigating through your phone's developer functions and checking boxes. If you haven't done this, it doesn't matter which streaming or original file you had; Bluetooth codecs compress it once more. Now, if you have selected this and have a powerful 330 kbps MP3 file, yes, there is a difference. A difference compared to CDs exists. It's not about missing frequency or audible distortion, it's about spatial detail. Just the positioning of band members, choir or orchestra, with the most noticeable impact in terms of depth. This was my unfair test – comparing the best Bluetooth's highest capacity MP3 with a CD played through a cable.

Oddly enough, although there is a difference, I have never abandoned listening to MP3s ripped from CDs and switched to a CD player. This is because the actual music experience doesn't differ much for me, even if the members of the band gain an extra half meter of space between them. Since not everything worth listening to is available on CDs, the inconvenience doesn't justify itself against the easily attainable difference in quality. Thus, music enjoyment can be overshadowed by chasing quality.

Unfortunately, the discussion is not even halfway through, and there are many more opportunities to degrade quality long before sound reaches our ears. The next point is the DAC (digital-to-analogue converter). Somewhere in your receiver/amplifier, there's a microchip that transforms the ones and zeros into an analog sound signal. Paths can diverge here, as audio can be distributed in digital form between the loudspeakers and parameters adjusted according to their characteristics. If you own a system like this, you're likely using active speakers or running as many pairs of cables to the speakers as there are loudspeaker units. However, more often than not, it's not like that, and if you have a microchip clearly defined by a trustworthy manufacturer, you can hope and believe that the digital sound file will be turned into a high-quality analog signal.

The conventional next stage is the audio amplifier. Trust me, this stage can be skipped entirely. Compared to the audio lost in initial compression and the audio lost in the final stages, modern amplifiers are of sufficient quality. The only real difference is convenience of use, meaning necessary and unnecessary additional functions. Following this sentence, there might be audiophiles among the readers, red-faced and ready to make angry comments, arguing that their experience is exactly the opposite. Firstly, they are right. Secondly, the nature of their experience is opposite – an amplifier can compensate for speaker shortcomings. If the speaker lacks dynamics, it naturally sounds better with a more dynamic amplifier. If the speaker's high frequencies are too sharp and skewed towards harmonics, a smoother-profiled amplifier can help to smooth them out, to name a few simple examples. Every deficiency can be compensated to some extent by the amplifier. In summary, a normal amplifier is not a source of quality loss, but an amplifier suitable for the speaker can help mitigate the quality losses of the speaker.

After that, the electrical signal enters the speaker cable. This topic has been widely debated on the internet, and to satisfy audiophile demands, some cable sets cost more than a TiFi loudspeaker with all its technology. However, it has not been scientifically proven that within the confines of a typical living space, the speaker cable significantly affects the sound. Simply put, the resistance, inductance, and capacitance of a 10-meter cable are negligible compared to the speaker's. They don't impact measurements. However, it has been established that poor contact significantly affects sound. Often, a new cable sounds much better, which can often be attributed to this issue. Thus, every couple of years, the loudspeaker cables should be disconnected, the back cover of the banana connector should be removed, and the connection should be checked for oxidation or near breakage. If so, the easiest solution is to cut off 10 cm and reattach the plugs. Looking inside expensive speakers, the cables are either soldered directly to the contacts or soldered to plug terminals. Thus, even for speaker cables, the most secure connection is a proper solder joint. Naturally, an exposed long cable can pick up unwanted signals, so it should be kept away from power cables. The cable shouldn't be too long, and a very long cable shouldn't be tightly wound (which rapidly increases its inductance).

And here we arrive at the masterclass of quality losses, the speaker itself. For while we had zeros and ones, which modern electronics master perfectly, and from this, an elegant electric signal, which modern electronics handle excellently as well, now we must convert electricity into sound. Now we enter the realm of electromechanics because, even today, a mechanically moving object is required to create sound waves in the air. Here, we have an immediate culprit for all distortions. The culprit is not lazy speaker or loudspeaker manufacturers. The culprit is physics. Quite simply, every speaker distort sound because it's not otherwise possible.

The first place sound enters is the crossover filter that divides frequencies between different loudspeakers. Regardless of the analog filter used, it starts removing frequencies from the sine wave by cutting out pieces. Additionally, they cause delays in lower frequencies. Schools of thought differ, some favor steep filters that affect the sound in the smallest frequency range possible. Some prefer gentle filters that impact the sound more cautiously but in a broader frequency range. Generally, extremes are better, and it's more challenging to maintain quality with filters of average aggressiveness.

Now that sound has been divided and shifted, the appropriate frequency range is presented to the appropriate loudspeaker. This is where things become quite complex, and there are numerous possible issues. Uneven movement of the loudspeaker diaphragm, bending of the diaphragm, inductance and mass inertia, sound caused by the elastic diaphragm surround, phase shifts of different frequencies, reflections of sound from all components, etc. When the loudspeaker diaphragm produces sound, it does so in both directions – forward and backward. Many acoustic issues are associated with this, which were somewhat covered in blog posts about frequency and wavelength. Generally, the biggest issue is the energy of sound that has entered the loudspeaker cabinet and wants to do something, whether vibrating panels, reflecting back through the loudspeaker, or in some other way. Of course, this doesn't occur uniformly but inevitably at some unwanted frequency, e.g., resonating with the room. Even sound waves moving forward interact with the loudspeaker cabinet and cause problems, and different loudspeaker sounds can interfere with each other if considering an example problem.

From here, we might think optimistically that now everything is in order. On the contrary, an even more severe or even worse source of distortion is still ahead. Acquiring a good loudspeaker can be done by paying. Engineers at the factory have worked hard and managed to minimize most issues to levels that are inaudible (like a mosquito's hum next to an air hammer). However, usually, no audio engineer has designed the room where you listen to the loudspeaker. This is an even larger and more powerful loudspeaker cabinet. For example, the loudspeaker is tuned in the factory to ±3 dB. A listening room can easily alter this for a particular frequency to ±10 dB, and if room resonance is hit, even more.

All of this text might seem quite discouraging. However, there are two significant rays of hope. Firstly, engineers can eliminate issues mutually. For example, most loudspeakers cannot present all the quirks that a distribution filter does with an electrical signal. So, in some cases, you can remove a chunk from the sound wave, and the final sound might not be significantly affected. Timing issues are more severe, and while solutions exist, they're not straightforward. Secondly, human ears adapt very quickly. So quickly, that if your home speaker has had an incorrect profile for years, all other speakers might sound incorrect. Let alone the fact that hearing can also detect and eliminate sounds appropriate to the room.

In conclusion, for high-quality music reproduction, the following are needed in order of importance:

1. Properly position the loudspeaker in the room. If necessary, address room acoustics.

2. Good-quality, high-end speakers.

3. The rest of the chain – make sure nothing goes wrong.

Notes:

As a warning, a note about the noise level of the amplification chain. All active components amplify previous stage default noise level among other signals. Therefore, the same amplification chain noise can be reduced if the first stages are amplified a lot and the final stages progressively less. For example, when sending a Bluetooth signal from the phone, there's no need to keep it at 10% and the final amplifier at 70%. Somewhere in that receiver is a DAC microprocessor that turns that Bluetooth into an audio signal and amplifies it according to the given level. If the signal's intended level is low, it will be amplified less. Noise is added to the signal. The next stage amplifies it...

A completely separate topic is devices that use psychoacoustic tricks and deliberate distortions. The goal is simple – to deceive perception and the brain by using various phase shifts, frequencies modulated over other frequencies, etc. To be honest, television and films are also such deception because we don't see moving pictures; we see rapidly alternating images. This doesn't stop me from watching TV. If such a device sounds good to you, then everything is fine, despite it intentionally distorting sound.

And, in reality, this serves as a guide to constructing good speakers. Yes, of course, problems can be masked and hidden. This way, a pretty good speaker can be achieved. But an even better speaker can be obtained by avoiding problems. Since you can't change the laws of physics, ingenuity and experimentation are required to put those same laws of physics to work for the sake of good sound.