Digital Amplifiers

Analog music signals have been electronically amplified since the development of the first electrical phonograph in 1925. Originally amplifiers employed vacuum tubes to boost the analog signal to an amplitude (voltage) that could move a loudspeaker cone. A much more recent development was the use of transistors to amplify these tiny signals. Both of these technologies are relatively inefficient and produce heat as a by- product of their design. In order to mass- produce analog amplifiers at a reasonable cost the tolerances of the parts employed are reduced. This results in an increase in signal distortion and degradation and a loss in quality.

The distribution of Digital Audio on CD's removed a very weak link in the audio signal chain and brought the quality of studio master tapes to the home. However the tiny audio signals produced by the DAC (Digital to Analog Converters) in the CD Player were still fed into an analog amplifier in order to be heard.

Now a revolutionary new technology called digital amplifier has come to the audio universe. Digital amplifiers make it possible for the audio signal to stay in its pure digital form through the complete audio signal chain to greatly enhance sound quality. In a pure digital amplifier, (one with a digital input ), there is no need for Digital to Analog Converters in the audio signal path. Digital Amplifiers actually synthesize the desired output signal directly on the speaker terminals, thereby creating a high-powered digital-to-analog converter.

Until very recently, the fully digital amplifier was only possible in laboratories, or in extremely expensive high-end audio systems. Now the technology has been reduced to just one or two chips, dramatically lowering manufacturing costs. In many cases this superior new technology can be incorporated into products even more inexpensively than the archaic linear audio amplifiers that will soon be known as "things of the past."

In case we haven't made ourselves perfectly clear, beware of digital amplifiers that only have analog inputs! These products are actually hybrids and are NOT pure digital.

Digital Compression

Originally most audio was recorded and distributed on CDs in the PCM format. The PCM file format consumes about 9 megabytes of file space for each minute of audio program length. Digital compression reduces the file size, and therefore the transmission time, of audio program material over a communications network such as the Internet.

There are two general types of digital compression - lossy and lossless:

Lossy Compression
In a lossy compression scheme, as the name implies, some of the original information is discarded when it is compressed. Therefore, it is impossible to produce an exact replica of the original audio signal when the audio is played. There are many different schemes of lossy compression available. These schemes generally provide varying compression ratios. The most popular of these, the MPEG Layer 3 (MP3) format, is commonly employed with compression ratios of up to ten to one. All lossy compression schemes add artifacts to the compressed audio. Artifacts are small imperfections created by the loss of the actual audio data. Although its quality may not seem that poor, the audio that has been processed by a lossy digital compressor is no longer "CD Quality".

Lossless Compression
Lossless compressors produce an exact replica of the original source. For example, the zip file format produced by the Winzip program on a PC produces exact copies of the original material that was encoded within the zip file. Fortunately, there is at least one lossless compression scheme available for Windows PCs. It's known as Shorten, an audio format that creates an exact clone of the original source. Lossless compression is the only way to preserve the "CD Quality" level of your program material.

Do we still need digital compression in this high-speed world? For the time being, the audio you seek may only be available in compressed formats like MP3. We are rapidly approaching the time when we won't need to compress the audio in order to save transmission time or conserve disk storage space.

One proponent of Lossless Compression is Etree.org a music distribution hub but not for audio that has been compressed in a lossy fashion like MP3 or AAC but for audio that has been compressed in a lossless way. Etree.org uses the Shorten (.shn) audio compression format because it creates an exact clone of the original source.

Digital Audio Sources

Presently we listen to digital audio on Hybrid systems. Digital signal sources must be fed thru Digital To Analog Converters then to linear analog amplifiers in order to be heard on a loudspeaker. Pure digital amplifiers break thru this last remaining weak link in the audio signal chain and make it possible to keep the audio in a digital state all the way thru the amplifier. Digital To Analog Converters are eliminated and there are many other sonic and financial advantages as well.

In order to have a purely digital audio system the program material needs to stay in its digital form through every stage of electronics from the storage device (like a CD) or transmission medium (like satellite signal) to the loudspeaker. This means either everything needs to be in one box like a DVD Player which includes a pure digital amplifier and feeds speakers directly or the device being used as a signal source needs to be equipped with a digital output.

The most common digital outputs used on audio devices are S/P DIF and TOS or TOS-LINK, AC3-LINK , USB and IEE 1394. Of courses there could always be new standards developed when needed. S/P DIF and TOS are very common and are included on virtually every new CD player and DVD player manufactured today. We can thank the MiniDisk (MD) for that. In order for MD recorders to record MD's they needed a digital signal source.  Kind of like a the which came first the chicken or the egg  scenario.  You need a digital output to record a digital MiniDisk. MiniDisks were touted by consumer electronics manufacturers to be the next personal audio platform but became overshadowed by the less complex personal MP3 player.

CD Players
Most new home style (non portable) CD Players come equipped with either a S/P DIF or TOS digital audio output. In the automotive arena almost no manufacturer  of automotive CD players equipps their CD players  with digital audio outputs. The notable exception is Clarion who has four CD changers sporting digital optical outputs (TOS). At least one automotive CD player manufacturer was aware (COOL) enough to include digital outputs on their CD players. This makes it much easier for pure digital enthusiasts to implement awesome audio systems in their cars.  All they need to do is add a pure digital automotive amplifier. Luckily there are at least 3 models of pure digital automotive amplifiers being manufactured today. Before you buy a new CD Player check it out to see if it is equipped with a digital audio output.

DVD Players
Virtually all DVD Players come equipped with either a S/P DIF or TOS digital audio output.  In the automotive arena almost all the DVD players come equipped with a digital audio output as well. Before you buy a new DVD Player check it out to see if it is equipped with a digital audio output.

SACD Players
Most Super Audio CD (SACD) players will come equipped with a S/P DIF or TOS digital audio output. The problem is the S/P DIF and TOS outputs will only work when you are playing standard CDs in the player. The SACD signal is a 1 bit Direct Stream Digital signal that is not compatible with S/P DIF or TOS.  At this time there is no digital output standard for 1 bit Direct Stream Digital digital audio so no high definition digital audio outputs are supplied.  IEE 1394 (Fire Wire) could easily transport the audio data if desired or yet another digital audio output hardware standard could be devised for 1 bit Direct Stream Digital. Before you buy a new SACD Player check it out to see if it is equipped with a digital audio output.

DVD-Audio
DVD- Audio is a competing standard to the Super Audio CD (SACD). Kind of like the VHS vs BETA phenomenon. DVD-Audio uses the linear PCM (pulse code modulation) approach to digital audio encoding. The SACD uses an alternative approach called Direct Stream Digital (DSD). The SACD format has several technical advantages. The SACD also has 1 logistical advantage to record companies. A SACD disk can be played in either a standard player or a SACD player so only one disk needs to be manufactured and distributed. Some new players will be able to play either SACD or DVD-A discs making the format war less of an issue. Virtually no DVD-Audio Players come equipped with either a S/P DIF or TOS digital audio output.  IEE 1394 will be used as the digital output medium in future players. Before you buy a new DVD-Audio player check it out to see if it is equipped with a digital audio output, and make sure it can play both SACD and DVD-Audio disks.

Mini Disk Players
Virtually every MD recorder comes equipped with a digital input so there would be no signal degradation when recording. Home style (non-portable) MD Recorders also come equipped with digital outputs as well. No Portable MD Players come equipped with digital outputs. One automotive MD player does come with a digital output however. Clarion makes an automotive MD Player with a digital audio output. Before you buy a new MD Recorder or Player check it out to see if it is equipped with a digital audio output.

DSS Satellite Receivers
Many satellite receivers come equipped with digital audio outputs. Before you buy a new DSS Receiver check it out to see if it is equipped with a digital audio output.

Satellite Radio
Virtually none of the announced satellite radio receivers will come equipped with digital audio outputs. All satellite radio receivers made for either the XM and Serius systems use chip-sets made by agere (Lucent) or ST Microelectronics.  Both of these satellite receiver chip-sets provide digital outputs. But it's up to the manufacturers of the digital satellite radio receivers wether they should include digital outputs on their satellite radio receivers or not. It is very important for "Digital" radio receivers to be equipped with either a Pure Digital Power Amplifier or at the minimum a digital audio output so that consumers will not be closed out using the receiver as a digital signal source for their pure digital audio system. One reason consumers will want to buy and pay for Digital Satellite radio is for the increased audio quality. By the time it gets to the receiver the audio signal has traveled more than 45,000 miles in a digital format it would be a shame if it couldn’t make it that Last Inch to your pure digital amplifier. Before you buy a new Satellite radio receiver check it out to see if it is equipped with a digital audio output.

Cable Boxes
Many cable TV boxes come equipped with digital audio outputs. Before you subscribe to a cable TV or cable DMX service check it out to see if the cable box is equipped with a digital audio output. It might make more sense to get a DSS receiver instead  if you're setting up a pure digital audio system.

Compressed Media (MP3 / AAC / WMF) Players
Virtually none of the portable MP3 / AAC / WMF Players on the market come equipped with digital audio outputs. A few manufacturers of Home style (non-portable) players include digital outputs. Before you buy a new MP3 Player check it out to see if it is equipped with a digital audio output.

Personal Computers
Virtually every computer on the market come equipped with some kind of digital input and output. The most common type is the USB or Universal Serial bus. Some computers like the Apple iMac and Sony VAIO come equipped with one or more IEE 1394 (Fire Wire) ports.  Both the USB and IEE 1394 (Fire Wire) ports can support the transmission of digital audio. The IEE 1394 port has enough capacity to transmit hundreds of simultaneous channels of CD quality audio or  SACD audio or even several channels of hi definition video. Digital audio output cards are available for Personal Computers that provide S/P DIF and TOS digital outputs as well. Before you buy your next computer check it out to see what kind of digital inputs and outputs it is equipped with.

New Devices
As technology progresses there will certainly be new sources of digital signals to consume. We should always be aware of the connectivity options available on new equipment we purchase so we can make the best choices. That digital input or output might not seem so important right now. But in the future you may be closed out of using your legacy equipment in a pure digital system if it lacks the proper digital inputs or outputs. Before you buy your next TV Set, VCR, PVR ect. check it out to see what kind of digital inputs and outputs it is equipped with.

Digital Video Sources

Digital Video Cameras
Most digital video cameras on the market have an IEE 1394 digital output. Some digital video cameras on the market have a digital recording medium like tape, Compact Disk or Mini Disk as well. Before you buy your next Hi Definition TV Set, VCR, or digital camera check it out to see what kind of digital inputs and outputs it is equipped with or what type of digital media it uses.

Digital Video recorders
New digital video recorders should have an IEE 1394 digital input and output.  Before you buy your next Digital VCR or PVR check it out to see what kind of digital inputs and outputs it is equipped with.

Digital Television Sets
New Digital TV sets and Hi Definition TV sets should have an IEE 1394 digital input and output.  Before you buy your next Digital TV sets or Hi Definition TV Set check it out to see what kind of digital inputs and outputs it is equipped with.