Digital Signal Processing – is it necessary in audio amplifiers?
The long and the short of it is no. For most professional audio engineers they can get the same result from a free standing unit which can also be rack mountable. I don’t use one, possibly as a result of using one a few years back which I felt was seriously very cheesy. I also have ahome theater system which sounds best in ‘unmodified’ 5.1. I am also a firm believer in that in the real world I want to hear the original sound track only in a magnified manner and not with cheap tricks and computer control. Having said that, there is a place for them and that would be with the audio engineer or in live recording. These units can be expensive though – the DSP pre-amplifier to me is the way to go if you do need the luxury of computer control. Home theater systems are often the chief offender – even some of the more expensive units.
What does DSP do?
Anyone knowing their way around a computer will have a general idea as to the merits of sampling, storing and changing the wave amplitude and frequency, with or without external modulation. Anything done in the digital realm can be classified as DSP and this can be audio or light. DSP can be used for reducing feedback howl on the stage as well by phase shifting the signal but this can be from the pre-amplification side and not the power amplifier. Again, a common misconception is that Class D power amplifiers are digital amplifiers. The reality is that as of now this applies to switching amplifiers only. In future this may change – in fact, it will change but the main advantage of Class D amplifiers are efficiency. There are many books written on the subject of class D amplifiers and digitising the partial or the entire audio spectrum which is most often used in the front-end and not the power stages. Gimmicky? In my view digital signal processing is just that when used for home use. I mentioned that for professional audio engineers DSP is a necessity – it is only because they know what the scope of the functions are and how to use them. I apply this equally to many non-professional audio people whom do not use the merits of DSP. However they don’t see this as a plaything but an advancement to their craft. DSP is an extremely useful tool in the hands of the right people. The Soundblaster Live card from Creative was a very popular card for the home user. For professional use you will need to go to Tom’s Hardware and read the reviews. Mac standards still seem to be the way to go. See ProAudioDSP.
The advantages (to name a few)
- Controlling phase shift – feedback howl
- Immunity to noise
- Filters – Large scale production is cheaper
- Feedback and remote control
Digital Signal Processing in general
DSP is here to stay, like it or abhor it. The simpler the better. Amplifier effects can be generated by your home computer – in professional audio amplifiers many of the functions are beyond the users level of expertise. This is not to say the user is a dumb animal – far from it. There are certain ranges of frequencies which suite certain loudspeakers better than other and it’s simplest form this would be highs, mids and lows. Most home users would not have the time or the inclination to stack amplifiers, set up the audio filters or have the space for multiple loudspeaker systems. Audio compression is best understood by professional audio’ists and should not be necessary when playing back program material from a CD or DVD. Who cares if it is valve, opto, FET or VCA compression? Some of the best sound systems I have heard had the least controls – straight from a moving coil pickup head.
Digital Signal Processing – the last word!
DSP is here to stay and the more gimmicks the manufacturers can throw into the mix the better it sells. Unfortunately for the home user most of this is totally unnecessary. According to a pro-audio expert friend whom does sound installations for the rich and famous, most systems sold are based on name brand and price – whether it is used properly or not is immaterial. Many times the speakers are fed anti-phase without the listener even detecting a problem in the image reproduction.
The only advice one can give to a person buying an entry level amplifier is to forgo the gadgetry and listen to it in it’s rawest form which is after all to amplify a signal to be driven through a loudspeaker. If it sounds like it’s playing in a coffee can, well all I can say is welcome to the modern home theater system.
Note: As an aside some of the best audio equipment is still manufactured by companies following old practices. With DSP one can disguise not so apparent problems with sound quality, dynamic range being one of them. If this weren’t true listen to your best audio material through a class-A amplifier and good headphones.
Further reading on Digital Signal Processing: Pre-emphasis and De-emphasis, compression and limiters, Audio Signal Processing.