System design criteria
What advantage does designing and creating an entire audio playback system offer?
Many times you will hear an audio system that has some components that are really good mixed with really bad. If you go to a HIFI shop you will be presented with a system composed of the brands the store sells. You may think that the high end audio store has put together brand x with brand y and z to give you the best sound, but sadly no. The system may have a $4000 cable and a $20,000 turntable with a $2000 loudspeaker. Not that price means anything. The point is, a properly designed audio system would balance the quality of each component in the playback chain to maintain the audio performance at no more than the required cost for such a performance at each point in the chain. Yes you can throw away that $1000 fuse, we will not need it, the $0.50 fuse will let us put and extra $999.50 towards the Loudspeakers, where the money will really pay off.
The front end of an audio system is the natural starting point for system design. Compatibility with older media formats as well as future media formats is important if you want to make adoption easy and cost effective. Older media formats include analog and digital sources. Some digital formats may only be available in analog format as an example SACD. Due to copyright only a closed propietary digital transport can play SACD in digital format and even then it usually fails to work if any components in the chain are not from the same manufacturer. The design of our system is to be open to maximize versatility and performance. Considering these requirements we have two choices a digital or an analog front end. If we use an analog front end then we will need a digital to analog converter for all of the digital media sources if they are not already so equipped. If we use a digital front end then will will need an analog to digital converter for all media players not equipped with a ADC. Now let us consider the balance of media sources. If you choose to play analog tape and vinyl as your main source with only occasional digital music then an all analog system would be a reasonable choice. The digital media will be converted once to analog. The worst system design would contain several conversions from analog to digital and/or digital to analog within the chain from media player to Loudspeakers.
Digital or Analog
When analog to digital or digital to analog conversion occurs some degradation to the audio stream occurs, this is certain. The level of degradation is dependent on the quality of the equipment used and the settings chosen. A low quality conversion is easily heard as such. A high quality conversion will have inaudible distortion to the original audio stream. The debate is over, it has been proven elsewhere, and I leave it to the reader to prove to themselves that an analog recording converted to digital and both played back in A/B would be impossible to pick out any difference between them. Even so to put an analog or digital stream through many conversions greatly increases the likelihood that degradation to the audio stream will occur. Analog components each add noise to the stream as a chain of analog components in the system increases so the signal to noise will degrade. Analog filters add phase shifts and time delays with each stage. Digital filters can have minimal phase shift and small time delay and have high roll off rates. Modern Audio Digital signal processors are superior to analog audio filters when used in Active Crossovers where high order roll off and linear phase is desirable. Thousands of successful all analog audio systems have been produced but few all digital systems exist. Lets design and build the ultimate (to date) Digital Audio system possible. The Digital Audio system would have a digital front end and remain digital to the Digital to Analog converter that drives the Amplifiers for each of the Loudspeaker drivers. The system would be as follows:
Digital Front end that would have analog inputs for tape, vinyl, microphones, guitars.... Many choices of analog media players. The front end would also be able to take in digital sources such as DAT, optical, coax....
Media players on a computer are very convenient music servers and this would also need to be incorporated into our system. The digital media formats should be lossless such as Flac so as to achieve the best results. Yes we can play MP3 but if a Flac version in 2496, 24 bit 96khz is available then use it. This brings us to the next problem, digital format, it is bad to change sample rates between stages in the playback chain. A
recording in 96khz played back at 44.1khz would degrade the audio steam significantly.
Sample rate and bit depth
The system should be designed so every part in the chain uses the same sample rate. I propose we use 24bit 96khz as it is a standard in the professional audio world and is easy to maintain.
In part II we put together a map of the system
Peter
