Digital provides the most practical, convenient and effective way to store and transmit music. Digitally stored music is usually stored and played back using disks such as CDs or streamed. The two main things which make up the quality of the sound from a digital source are the type of file the audio is stored as, and the performance of the Digital to Analogue Converter. The DAC translates the data back into an analogue waveform which can then be amplified and heard.
Although there are High Resolution audio formats which are better quality than CD. CD quality is still very good. Unless you have ever listened to a high-end quality CD player, then you may not have actually experienced the full capabilities of CD recording.
A CD player has the mechanism to play and read the CDs, as well as a dedicated DAC to output the music as an analogue signal.
A CD transport features just the mechanism to read the discs and relies on an external DAC to work. It outputs the digital signal using either a coaxial or fibre-optic cable to your DAC.
There are a few CD players on the market which also have digital in-puts, allowing the built-in DAC to be used to replay other digital audio sources. There are even some which feature streaming capabilities.
Whether you decide to use a basic CD player with built in DAC which will just play CDs, a separate DAC and CD transport or an advanced CD/DAC/Streamer combo is down to your own preference, budget and requirements.
As well as regular CDs there are other CD formats available too:
- HDCD – High Definition Compact Disks
You might have some of these already and not know! Where a regular CD is 16-bit HDCDs have an extra 4-bit encoded in them. If you play an HDCD on a non-HDCD player, it will simply ignore the extra data. A CD player with HDCD will play HDCDs at the higher 20-bit quality.
- SACD – Super Audio Compact Disks
This is a high resolution audio format which uses a format called Direct Stream Digital (DSD). This provides more accurate audio reproduction that CDs which use a format called Pulse Code Modulation (PCM). Instead of the 44.1 KHz sampling rate available on CD, SACD sample at 2.8224 MHz. SACDs have the same data capacity as DVDs. A regular CD player cannot play SACDs, while a SACD player is backwards compatible and can play CDs. There are some 2-layer disks available which have both the SACD DSD format and the PCM format on one disk. These will play on a regular CD player.
Whichever type of player you choose, it is worth baring in mind that the quality of the transport mechanism will have an effect on the audio quality. The mechanism is such a fine, intricately made thing, with many moving parts working together.
The track of a CD is a tiny fine line which is read, by a laser, from the centre of the disk to the edge. Imagine the gears on a bicycle. When the laser is reading the track closer to the centre of the disk, the CD must be spinning at a slower speed than when it is reading the track at the edge of the disk. Indeed, the CD’s rotation speed has to adjust very finely and consistently to match the part of the disk which is being read at that specific time. It varies between 200 and 500rpm.
The CD is never clamped perfectly centrally within the player and not perfectly balanced. This means that as the track flies past beneath the laser, it weaves from side to side both vertically and horizontally. The mechanism which focuses the laser’s beam has to constantly adjust to allow for this.
A good CD mechanism will be able to cope with these tasks and produce far superior results than a cheap CD player which is likely to use the same kind of basic mechanism that you may find in a PC CD-ROM drive.
Much of the music we listen to these days is streamed digitally. This can either be from internet based steaming services or from your own music library stored on either a computer or server on your home network.
There are a few ways to do this:
- One of the simplest ways is to use a Bluetooth DAC and a tablet or mobile phone. The DAC plugs into the connections on your amplifier. You connect your device to the DAC wirelessly using Bluetooth. Then whatever you play on your device will play through your HiFi. There are various apps available to browse and play music either from your own collection or from the streaming services or internet radio.
- A WiFi DAC. This works the same way but uses your WiFi network instead of Bluetooth.
- A HiFi streaming device. These connect to your home network and have their own screen and remote control, so may be controlled without using a smartphone. Although the app is usually a better way to browse for music. They usually have a good DAC built in.
- Your smart TV, Bluray or Apple TV, Chromecast etc. You should use any of these with a decent, separate DAC for best results.