Hi-Res Audio: Everything a Listener Needs to Know

We've all encountered the "Hi-Res" logo on various audio products, but what exactly does it signify? Let's delve into the definition of Hi-Res Audio and explore the criteria for a product to attain Hi-Res certification.

In 2014, the Japan Electronics and Information Industry Technology Association (JEITA) formally defined High-Resolution Audio. According to JEITA's standards:

High-Resolution Audio entails a sampling frequency or rate surpassing the CD specification, with neither parameter falling below CD standards. The CD specification entails a sampling frequency of 44.1kHz and a bit depth of 16 bits.

Examples of Hi-Res Audio configurations include:

• 24bit/44.1kHz (exceeds or matches CD quality) → Hi-Res

• 24bit/48kHz (exceeds or matches CD quality) → Hi-Res

• 16bit/96kHz (matches CD quality) → Hi-Res

• 24bit/96kHz (exceeds CD quality) → Hi-Res

• 16bit/48kHz (CD-equivalent quality) → Not Hi-Res

Although JEITA defined the standard, the logo was crafted by SONY and widely employed with their products. Subsequently, the Japan Audio Association (JAA) collaborated with SONY to transfer the logo trademark, enabling JAA to employ it as a certification mark for Hi-Res Audio equipment.

JAA has established specifications that must be met for manufacturers to display the Hi-Res logo on their products post-licensing agreement with JAA. The stipulated specifications encompass both analog and digital processes:

Analog Process:

• Microphone response performance: 40 kHz or higher during recording

• Amplification performance: 40 kHz or higher

• Speaker and headphone performance: 40 kHz or higher

Digital Process:

• Recording format: Capable of recording in the 96kHz/24bit format or higher

• I/O (Interface): Input/output interface performance of 96kHz/24bit or higher

• Decoding: File playability of 96kHz/24bit or higher (FLAC and WAV required)

• Digital Signal Processing (DSP): Processing of 96kHz/24bit or higher

• D/A conversion: Digital-to-analog conversion of 96 kHz/24 bits or higher

We have defined Hi-Res Audio and Hi-Res audio certification on products but how does this translate to audible difference to the listener. To better understand this we need to look into the two parameters that makes up the specification namely:

1. Sampling Frequency

2. Bit Rate

Lets look at these two factors one by one:

1. Sampling Frequency

When analog signal is converted into digital signal this determines the number of times the signal amplitude is read digitally per second. The below illustration by SONY is quite helpful in understanding the concept as it shows a sound wave within same time frame with B and C showing the digital samples taken at different sample rates:

• A: original analog recording

• B: CD: 16 bit/44.1 kHz

• C: High-Resolution Audio at 24 bit/96 kHz

This is a bit confusing but from a music listeners perspective there are only two things we need to keep in mind

1. Humans can hear from 20Hz to 20kHz so the highest frequency we can hear is 20kHz

2. Nyquist Theorem states that to get a faithfull representation of the measured signal the sampling rate should be more than double of the highest frequency component in teh signal.

Under the above two conditions to capture the highest frequency of hearing which is 20kHz we need to sample at a minimum double that and to have a buffer the most commonly used sampling frequency is 44.1kHz and this was used for CDs as well.

2. Bit Rate :

This is a bit more complicated to explain, from sampling rate we have decided the minimum sampling frequency required to capture the highest frequency we want but to what accuracy we want to capture this depends on the bit rate. Bit rate determines how close to the actual analog signal amplitude value is our measurement captured or to what precision we capture the amplitude value.

As the analog value cannot be capture in absolute precision we need to decide how close we want to capture so the the rest can be ignored. The error between this and the actual analog signal leads to noise being introduced in the digital signal which is termed as Quantization Noise. The aim here is to capture as close as possible to recreate the music with inaudible noise. Lower the bit rate the higher the error. So to determine how much noise is actually audible to a listener we use Signal to Quantitation Noise Ratio(SQNR) which determines the dynamic range of the measured digital signal. There is only one variable in the equation for SQNR which is the Bit rate

SQNR = 6.02Q

Q= Bit rate

From the above with 16bits we get 96db and for 24bit we get 144db but what does this translate to in real world, for a digital music recored at 16bits if we are in a quietest room we will need to raise the SPL to 96db to start hearing the noise and that too only when the music is almost silent. As most of our listening is in average rooms with ambient noise of minimum 30db to hear this is the quietest sections of the music we should be hearing music at 126db which is almost painful. So the higher the Bit rate the higher dynamic range can be captured. Other than Classical music most other genre do not have high dynamic range and even classical we dont need more than 40db.

Both of these factors also determines the size of the digital file thus affecting the storage capacity required. For stereo recordings the kilobits required per second is determined by multiplying the bit rate with sampling rate and then doubling the value:

• 16bit/44.1kHz = 16x44.1x2 = 1411kbps

• 16bit/96kHz = 16x96x2 = 3072kbps

• 24bit/44.1kHz = 24x44.1x2 = 2131kbps

• 24bit/96kHz = 24x96x2 = 4608kbps

From the above its quite evident that how much more music data is available in a Hi-Res file for the equipment to more truthfully reproduce music closer to the original even compared to a CD let alone a 320kbps mp3.

Ultimately, the quality of mastering plays a pivotal role in extracting the best from any music file.

Proficient mastering ensures that the nuances of the recording are preserved and enhanced, allowing listeners to experience the intended sound quality and richness of the music. Without skilled mastering, increased dynamic range and fidelity, may be undermined, leading to a suboptimal listening experience. While high-resolution audio offers the potential for increased detail and fidelity, it's the mastering process that truly brings out the best in the music, ensuring that it shines across all playback systems and formats. Without proficient mastering, even the highest-resolution audio files may not reach their full sonic potential or connect with listeners as intended.

The question arises: do we truly require this level of data and the associated storage? For most listening purposes, a digital file encoded at 16 bits with a 96kHz sampling rate suffices. However, CD quality (16bit/44.1kHz) remains ideal for many listeners, with perceived advantages above this being minimal.

My perspective aligns with the sentiment of many audiophiles who prioritize achieving CD quality in their digital audio setup. Maintaining CD quality ensures a high standard of audio fidelity while balancing storage efficiency and equipment capabilities. Anything beyond that could indeed be perceived as a luxury, offering marginal improvements in audio quality that may not be discernible to the average listener.

In summary, prioritizing better-mastered music over high-resolution audio files can lead to a more fulfilling and immersive listening experience, where the quality of the mastering plays a pivotal role in shaping the sonic landscape of the music.

While numerous online resources delve into these concepts, for a comprehensive understanding of the analog-to-digital conversion process, consider exploring Akash Murthy's insightful YouTube playlist on Digital Audio Fundamentals.

Take your time to engage with each video in the listed order for a thorough grasp of the subject.

Digital Audio Fundamentals by Akash Murthy