Noise Floor : Analog vs Digital

not really nTrack related…but…

Just curious, when I run my Tampa preamp using the analog lines, the noise floor is around -62 db in the nTrack VU meter. When i use the SPDIF line, it’s around -61db. I would have thought that the digitial line would have been a tad more quiet…not this other way around.

Does that mean that the converters on the Echo MIA card are ‘quieter’ than the Tampa conveter?

This really isn’t an issue, just trying to learn.

It probably has nothing to do with the convertors… if you have preamps in those devices (which you do) they are what is creating the noise. If you were to somehow disable the preamps, you should have near silence.

Right. With digital, there are two kinds of “noise floor”. The first, the one we normally mean by the term, is the amount of noise when there’s no signal. With digital, this is minus infinity (meaning, none at all). Any noise during silence is either a bug in the data processing or came from analog gear.

But whenever there’s a signal present, there also is a meaningful S/N ratio, which doesn’t make sense if the noise floor is zero. That’s because whenever there’s signal, there’s also roundoff error for each sample, called “quantization error”, and that makes “quantization noise” in the signal. The level of this noise depends on the sample bit-width; it’s roughly -96 dB for 16 bits and roughly 144 dB for 24 bits.

Just rambling on a tangent – Bubb answered the question!