reignofchaos
Well-Known Member
Prem has answered the question in the best possible manner. Mathematically any band limited signal can be represented by a sum of a series of sinc functions and a set of coefficients. To reconstruct the analog signal from these coefficients, one needs to be able to generate a perfect impulse which is known as a delta Dirac function. However a perfect impulse is impossible to generate. Most DACs approximate this using a square wave which causes aliasing and multiple harmonics of the original signal appear at the output. So this output must be filtered again to remove this spuriae. To do this DACs have a brick wall filter that removes content above 20khz or half the sampling rate at the output.
However these filters actually have a roll off and are not the ideal theoretical brick wall as it is impossible to engineer the same. Any filter rings or causes distortion. A traditional filter would actually cause something called pre ringing and post ringing. Pre ringing happens before the output and post ringing after the output. Think post ringing as the sound of a bell. After the bell rang, it smoothly decays and then stops. However pre ringing is an unnatural phenomenon - it is sort of effect before cause. To combat this meridian and a few others designed something called a minimum phase or apodizing filter. These filters avoid pre ringing at the cost of slightly increased post ringing and sound more natural. Pre ringing is what people associate the bright digital annoying sound to.
In addition to all this there is the sound of the DAC itself based on architecture - multi bit or delta sigma or hybrid. This profoundly affects the quality of output.
However these filters actually have a roll off and are not the ideal theoretical brick wall as it is impossible to engineer the same. Any filter rings or causes distortion. A traditional filter would actually cause something called pre ringing and post ringing. Pre ringing happens before the output and post ringing after the output. Think post ringing as the sound of a bell. After the bell rang, it smoothly decays and then stops. However pre ringing is an unnatural phenomenon - it is sort of effect before cause. To combat this meridian and a few others designed something called a minimum phase or apodizing filter. These filters avoid pre ringing at the cost of slightly increased post ringing and sound more natural. Pre ringing is what people associate the bright digital annoying sound to.
In addition to all this there is the sound of the DAC itself based on architecture - multi bit or delta sigma or hybrid. This profoundly affects the quality of output.