[sdiy] Harmonic bandwidth

[Nicholas Gregorich]

Richard Wentk wrote:
> 
> On 9 Jan 2008, at 19:22, Nicholas Gregorich wrote:
> 
>> When I did my test in MATLAB the data was generated and summed in 
>> 64-bit floating point and re-quantized to 16 bits for stuffing into 
>> the soundcard.
> 
> Was this with dither or truncation?

I read through MATLAB's documentation and didn't find anything specific 
so it must be truncation. This is not something I've looked into much, 
but I do understand the concept of dithering.

> Q-noise will be semi-correlated with any sine signal. Also, people tend 
> not to find sine distortion very audible - up to 10% THD is 
> unobjectionable, depending on the kind of THD. Most (affordable) 
> speakers produce a couple of percent of THD, so for a very accurate test 
> you need top of the line monitors.

One thing I noticed about the quantization noise is that it depends how 
the data is quantized: ceiling, rounding, or flooring. Ceiling and 
flooring have a lot less correlated distortion while rounding gives a 
nice harmonic series. I've been told most systems use flooring for 
performance reasons, but this might be true in communications more so 
than audio systems.

> Music tends to be more revealing. Features like dither and jitter make a 
> *huge* difference to sound quality, even though they measure around +/- 
> 1LSB in a digital system.

I was interested in jitter awhile ago but didn't find what I was looking 
for. What are the obvious jitter effects playing back a CD?

Nick.