Digital audio that really sounds better
If you only listen to digital music in 128 kbit / s (bps) AAC or mp3 format on a portable audio player such as an iPod, you will be moving away from real music.
You can understand the sound that is played by connecting an iPod to an audio device by comparing the sound of the original CD with a normal audio device. And there is digital audio with even better sound quality than CDs. It is a big mistake to think that mp3s are the sound quality of digital audio and that digital audio sounds better.
When a record company digitally records a musical performance, it is common to adopt the PCM (Pulse Coded Modulation) method or the DSD (Direct Stream Digital) method. Those recorded with PCM will eventually be sold as CD and DVD-Audio. What DSD records is sold as SACD (Super Audio CD).
In PCM, the sample rate (rate) and the number of sample bits are determined and recorded. The term sampling frequency is independent of the frequency of the sound and is the number of times a sample is taken per unit of time. The unit is “Hz”, and the higher this value, the more faithful to the original sound, but the larger the data size. For example, 44.1 kHz is selected for CD and 96 kHz or 192 kHz for DVD-Audio. DVD-Audio uses DVD to store large amounts of data. A 44.1 kHz CD can express signals (sound) up to a frequency of approximately 20 kHz. The sound that humans can hear is said to be up to 20 kHz, but the sound of a real musical instrument includes much louder sounds, and when played up to such a high range, the sound quality clearly improves. It has been confirmed that it will be done. With a sampling frequency of 96 kHz, signals up to 48 kHz can be expressed and the tones of musical instruments and voices can be reproduced more faithfully.
On the other hand, the number of sample bits is the number of quantization bits, which determines how many bits the sampled data is represented. The more bits there are, the more faithful the original sound will be, but the larger the data size. If the number of bits is small, the reproducibility of a small signal (sound) deteriorates. The number of bits on an audio CD is 16 bits. If it is 24-bit, it can be expressed with 256 times the precision of 16-bit.
The high-quality PCM digital audio format is 24-bit uncompressed, 96 kHz (2496 for short), or 192 kHz. However, only DVD-Audio or songs sold by Onkyo Marketing on the “e-onkyo music store” website can be purchased in this format (Fig. 1). To play DVD-Audio, you need a multi-format player such as the Pioneer DV-696AV. On your computer, a sound card such as Sound Blaster Audigy 2 is supported. DVD-Audio playback devices are listed on the DVD-Audio website.
Figure 1 ● Website of the e-onkyo music store that sells high-quality 24-bit 96 kHz music files
[Click the pic to enlarge]
DSD, on the other hand, is a completely different method from PCM and uses a delta-sigma modulation method. To put it very roughly, a bit transitions between Low and High states at a very high speed to express the pitch of the sound. It is a method that expresses the magnitude of the audio signal by the density (shading) of a 1-bit digital pulse. When the level of the original sound is high (the sound is high), the high state becomes lower, and when the level of the original sound is 0, it is Low and the number of High will be the same. The sampling frequency of SACD is 2.8224MHz (CD = 64 times 44.1kHz). Sound quality far exceeds that of a CD with a frequency response of 20 kHz and a dynamic range of 94 dB, with a frequency response of more than 100 kHz and a dynamic range of 120 dB or more (the dynamic range it’s wide to loud and quiet sounds). So the bigger the better). A high-speed CPU is required to handle DSD in a personal computer, and the Sony VAIO Type R, Type H, and Type V announced in September 2005 were the first to be equipped with DSD record / playback functions. SACD playback is also not possible with these models.
Requires dedicated hardware
To play the 2496, etc. With good sound quality, the personal computer’s audio hardware needs to be upgraded to 2496-compatible high-quality sound. The most popular audio hardware for personal computers is the IEEE1394 interface. It is convenient because it can be connected with a single cable.
I connected audio hardware for a personal computer and compared 2496 and 1644.1 (normal CD sound quality). The audio hardware tested is as follows (Fig. 2).
・ RME Fireface 800 (about 210,000 yen)
・ RME Hammerfall DSP Multiface (PCMCIA)
・ TerraTec P
