What is Audio? Understanding Audio Mechanisms and Technologies
Music has become an intimate part of our daily lives, with music streaming services and video sharing sites making it easy for users to listen to their favorite music anytime, anywhere. What’s more, recent advances in technology allow high quality audio to be played even on small portable devices such as smartphones. And the emergence of 5G in the near future is expected to remove all restrictions on communication speeds and capacities. This will allow everyone to experience realistic, powerful sound at home or on the go, including in high bandwidth applications such as VR.
In this article, we will focus on how sound is played back and explore the technologies hidden behind the music we enjoy everyday.
1. The 3 elements that make up audio
In everyday life, the word ‘audio’ is often used casually to refer to speakers and other related components. However, audio can roughly be divided into 3 primary mechanisms (devices): player, amplifier, and speaker.
1) The player reads the sound source stored on recording media
Music playback begins with reading the digitized audio source. The player fulfills this role by reading recorded media information (sound source) and converting it into electrical signals. How this information is read depends on the recording medium, such as using a needle for records and a laser for CDs. For digital sound sources stored on CDs and various types of memory, semiconductors designed specifically for audio (i.e. servo ICs that read audio data stored on CDs and audio SoC that read audio sources in memory) are responsible for extracting music information. These ICs are provided to audio manufacturers by semiconductor suppliers like ROHM.
The digital sound sources read from the recording medium remain digital or are converted into analog signals using a DAC (Digital to Analog Converter), then passed to the amplifier (described below). Particularly when using a DAC, it is extremely important that the analog signal is converted without degrading sound quality, which is why the DAC is said to be the component that has the greatest effect on sound quality.
2) The amplifier amplifies the signals read by the player
As its name implies, the amplifier (amp for short) amplifies the signal read by the player so that it can be reproduced as audio (sound waves). To drive the speakers, the signal read by the player must contain a large amount of energy. The amp accomplishes this by increasing the signal waveform while changing it as little as possible.
Like the telephone (messaging) game, the greater the number of intervening processes the more likely the original sound source will be degraded (changed), so the performance of the amp (good or bad) will have a large effect on sound quality.
3) The speaker converts the audio signals to actual sound
Speakers are perhaps the most well-known audio component. They are responsible for turning electrical signals converted and amplified by the player and amplifier into energy used to vibrate the air to create sound waves that can be heard by the human ear.
Although players and amps share similar form factors, speakers come in a range of shapes and sizes and utilize a variety of structures and materials. The general mechanism will be described below.
Electrical signals transmitted from the amp drives a unit within the speaker. Simply put, this unit pushes air by moving internal components in accordance with electrical signals using a mechanism of permanent magnets. The component that actually pushes the air is called a diaphragm, which typically features a cone- or horn-shaped profile. In addition, some higher end speakers use multiple units called ‘drivers’ to cover the low, medium, and high frequency range.
And similar to instruments such as the flute, piano, drum, or guitar, sound is greatly enhanced by resonating (bouncing) within an enclosure (housing that makes up the instrument). As a result, a wide variety of enclosure designs exist depending on the speaker type.
Component, PC, and smartphone speakers utilize all 3 elements
As we have explained thus far, music is played by combining players, amps, and speakers. All of these elements together to make up an audio system.
But how do the speakers in smartphones, PCs, and component systems work? By integrating a number of functions from the start.
Smartphones and PCs
These devices include all functions of a player, amp, and speaker in a single unit. This allows users to connect headphones by outputting only the speaker function.
These systems provide a separate player, amplifier, and speaker as one set.
2. Everyone has probably heard of ‘sound quality’, but few understand its meaning
Perhaps the most popular audio system for many these days is the combination of a smartphone and headphones. Looking at electronics retailers and online sites, we can see that a variety of products and brands are sold, ranging from thousands to hundreds of thousands of yen. And when making a purchase, isn’t sound quality among the most important features considered?
However, if asked the meaning of sound quality, most people would have a hard time answering (and the answers will inevitably vary from person to person). Also, as explained earlier, many mechanisms and devices are required before music is played. Consequently, sound quality not only involves the performance of the headphones, but the entire audio system as well, including the sound source.
Next, let’s consider sound quality. Here, we will look at both the relative and absolute definition.
The elements that everyone commonly thinks of when imagining sound quality are considered ‘absolute’. One thing that must be mentioned at this time is that sound sources can be recreated faithfully. This means that the recreated sound is not distorted, the entire range can be accurately reproduced, and there is no harsh noise.
Now, let us consider the case where the sound source itself is not faithful. For example, importing a CD on a PC and converting it to another format such as MP3 may cause it to be irretrievably compressed (but providing the advantage of a smaller file size). A similar analogy is compressing a high resolution image for the purpose of attaching to an email or posting on social media.
Unlike the absolute definition that everyone commonly agrees upon, an interesting aspect of sound quality is that the definition can also differ depending on individual preferences, ideals, the type of music often listened to, and other factors. This is referred to as ‘relative definition’.
For example, looking at the packaging for headphones, you can see buzz words like ‘clear sound’ and powerful deep bass’. But if you think about it, is the sound quality better if the audio is clear or has deep bass? This is the part where the evaluation will change depending on the individual.
Deep bass is ideal when listening to pop, R&B, hip hop, and dance music. But when listening to orchestras and symphonies, it is more important to clearly reproduce audio in a variety of ranges and timbres to express the complex interplay of different instruments and achieve an immersive soundstage that provides a greater sense of realism - as if the performance was live, happening right in front of the listener.
In other words, sound quality is often defined based on listening preference, which depends in large part to the type of music being played. This is in addition to being able to reproduce the sound source accurately, of course.
3. Sound quality is determined by a 1cm2 area of electronic components
To reiterate, recorded audio is converted to data and played back by the audio system. For this reason, as mentioned earlier the sound source, player, and amp have a significant effect on sound quality.
Although not an audio equipment manufacturer, ROHM supplies a wide range of electronic components used in audio players and amplifiers, including high-end systems and car audio/navigation systems. In particular, our volume control ICs and DACs are class-leading products that feature extremely low noise and distortion, two of the most important characteristics for improving sound quality in audio equipment.
Lastly, we will touch on the driving force behind the production of these products by ROHM. Underscoring this is a Quality First mindset. ‘Quality is our top priority at all times’ has been our company mission from the very beginning. Based on this concept, we strive to thoroughly improve quality in all product aspects. At the same time, ROHM employs many highly experienced engineers dedicated to improving the sound quality of audio equipment.
For audio-specific products, we are continuing to refine our sound quality design technology and have identified 28 parameters shown to have a significant effect on sound quality. Product development is implemented with the purpose of increasing sound quality in terms of resolution, realism, power, and other parameters not only through circuit and mask designs, but by controlling audio quality parameters related to wafers and packaging and by repeatedly carrying out real-world listening evaluations at the prototype stage.
Click on the links below to learn more about ROHM’s considerable activities and contributions to the audio sector.