So ... taking this above ^^ example ^^ ..... and assuming
(a) these figures measure and represent the exact same thing
(b) all other things in the modeler are equal and
(c) the guitar used in each is identical
Does the higher value -or- the lower value have *any* real world, noticeable / audible impact on the tone, dynamics, "feel" etc..... of an electric clean or dirty guitar signal played through each option (?)
Ben
The product with 101dB will have 22dB more "hiss". 101dB is actually quite poor by modern standards.
This is a fundamental part of mixed-signal design but apparently is difficult for people to understand.
Here's an example:
Assume the maximum input level of a guitar processor is 0dBv (1V). Assume that the processor has unity gain when there is no amp model between the input and output and the input is shorted. Now assume that the processor is connected to a sound reinforcement system such that 0dBv in achieves an SPL of 100dB. Assume that the sound reinforcement system adds no noise of its own.
Now, if the processor's DR is 100dB the noise out of the sound reinforcement system will be 0dB (inaudible).
If you then put an amp model into the processor with a gain of 60dB, which is not an unusual amount of gain, the noise out of the sound reinforcement system is now 60dB. That's pretty audible. Equivalent to normal conversation levels. So you're sitting there with your guitar's volume off and your speakers are going "ssssssss". It's further exacerbated by the fact that the noise is "white". Human hearing is pink which causes white noise to be more noticeable in the high frequencies. This is why things like pre-emphases/de-emphasis were invented. To reduce the perceived loudness of white noise.
If the processors DR is, however, 120dB the noise out of the speakers is now only 40dB which is much less audible.
The noise is also audible when playing lightly or rolling off the volume. If the DR of the processor is worse than the self-noise of the guitar then the processor's noise will dominate. Ideally the processor should have a DR that exceeds the DR of the guitar.
101dB is poor. A typical guitar at room temperature is about 115dB. This means the processor's noise will dominate. 123dB is excellent and the processor's noise will be very low.
Now, obviously interference (hum, EMI, etc.) reduces the DR of a guitar but interference is almost always periodic. Humans perceive white noise in the presence of periodic interference. IOW we still hear the hiss. 60Hz hum doesn't mask it. We hear "zzzzzzzz" plus "ssssssss".
There are several ways to improve the DR of a processor:
1. Use multiple channels in parallel on the A/D. Every doubling of the number of channels improves the SNR by 3dB. Some AKM products allow you to do this right in the chip so you don't have to drive multiple inputs thereby reducing cost.
2. Use pre-emphasis/de-emphasis techniques. Boosting the high frequencies in the analog domain and then cutting them in the digital domain. This reduces the perceived hiss.
3. Use dual-gain techniques. Use two channels on the A/D where one channel has more gain than the other. This is similar to what digital cameras do to reduce noise.
4. Use a combination of the above.
The analog signal path is also important. You must use quality op-amps and, ideally, true differential design for best performance. But this adds to the system cost.