Definition of sampling bits, sampling rate and bit rate in audio (transfer) Part 3
1. Why do many professional standards reach 24bit/192KHz?
It is now common to use the 48kHz or 96kHz recording rate in engineering, and only convert to the 44.1kHz CD format during the final mastering process, which reduces distortion caused by multiple sample rate conversions.
In the field of computing, the AC97 specification, which is an audio hardware codec standard, only specifies 48 kHz. This causes nearly all input and output signals to be resampled (the professional term is called sample rate conversion, or SRC). SRC generally causes loss of sound quality, and the simpler (ie poorer) SRC algorithms can cause significant deterioration of sound quality. But this is already a fait accompli.
2. Since 44K is enough, why use 192KHZ to record?
First of all, 20kHz is just the hearing threshold for most people, i.e. the human ear is very insensitive to sounds above 20kHz. Insensitivity to attention does not mean a total inability to perceive. The tones of most musical instruments (especially pianos and strings) are rich in higher harmonics, known in musical terms as higher harmonics. CD audio with a cutoff frequency of 22.05 kHz gives people who are used to listening to real instruments an unnatural feel, especially in the high frequencies, because the Nyquist cutoff frequency distorts the signal from harmonics. of higher frequencies.
Second, digital recordings often require post-processing. Audio processing can introduce more distortion into the signal, including signal distortion, spectral aliasing, and more. If the original signal is only sampled at 44.1 kHz during recording, it must be upsampled before post-processing to expand the sample rate. Since this expansion is “fake”, there is really no more useful original signal, and the quality of the upsampling algorithm will also affect the distortion of the original recording signal, so this approach is undesirable. Therefore, it is common practice to sample at a higher frequency.
In today’s fully professional digital recording studios, recording, mixing and mastering are no longer compliant with the CD standard, instead the HD audio standard is preferred. which:
Use 24Bit 48KHz, 24Bit 96KHz, 24Bit 192KHz three specifications to record, of course, 24Bit 48KHz is used by some small recording studios, because their processor resources are limited. And all the big recording studios use 24bit 96KHz and 24bit 192KHz for recording.
So what are the benefits of such a recording specification?
1. Comply with HD audio standard, which is also the main standard in the future. The finished product can be directly applied to HDCD, DVD-Audio, Blu-ray disc, digital music download business and digital player business to media.
2. Fully take care of the digital video and video business, and the multi-channel film and video will adopt the HD audio specification. Including the use of portable mobile digital video equipment.
3. Fully take care of the consumer audio playback business, such as: Intel HD-Audio audio standard, AC97 audio codec, MP3 / mp4 / phone / game console portable audio highest quality audio playback.
Currently, the highest quality standard in the professional recording industry is: 24 bits deeper than a specific point, 192000 Hz sampling rate, referred to as “24 bits/192 KHz”. Of course, this standard will continue to improve in the future, and it is also possible to move towards 32Bit 384KHz.
In fact, the (genuine) products sold in the current CD market are usually HDCD discs at the lowest level, when you buy discs, you find that they are basically HDCD logos, that is, a CD contains two audio tracks: Normal CD track and HDCD track. The CD track records a 16-bit signal at 44.1 KHz (this is the compatible content on this disc, considering early CD players), and the HDCD track records a 24-bit signal at 96 KHz ( this is the main content of the disc). Ordinary CD players can only play CD audio track signals, and HDCD audio tracks require an HDCD player to play (in fact, most DVD players today can play HDCDs, and modern computers work even better).
