gregorio
Headphoneus Supremus
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- Feb 14, 2008
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I have 4 of those boxes with 4 inputs and 4 outputs and also wanted to try to loop a stereo signal through them all twice, so that it passes 8 AD and DA conversions in a row. I figured that if that doesn't give a clear audible difference then there is no need to worry at all about one such a box in the chain.) ...
Just in case you are interested, this is the little 4 in 4 out DSP box I was talking about before, costing 77 Euro's: https://www.thomann.de/gb/the_t.racks_dsp_4x4_mini.htm ... It has a number of standard functions like delay and PEQ that can be configured from a pc via USB. The default settings are such that the signal passes unchanged, but it will always pass the AD and DA conversions and has some level drop that I counteracted by setting the ouput gains at about +7 dB (only for comparison, and while making sure I don't input a level that could cause clipping).
I've never come across that unit before. Obviously it's a consumer unit due to the connection type, plus I can't think of any professional situation where it would be of any use. Standard procedure when testing pro AD/DA units is to loop-back the stereo signal 10 times, in order to make the difference audible! With a relatively cheap consumer unit, especially as it's level appears to be considerably lower, fewer loop-backs might do the trick. I'm not sure what's causing the level drop by the way, although most likely it's one of two possible explanations: 1. It's reducing the level to give itself headroom for adding DSP or 2. You're feeding it a single-ended input, which would be roughly 6dB lower than the balanced input it's expecting.
But I was thinking maybe there is a more general set of audio fragments that in general maximises the chance of finding any differences in any blind comparison listening test. So that's why I asked the question: where could I find such a set of audio fragments?
There's not really a general set of audio fragments. We (audio engineers) each tend to have our own individual sets, which comprise a number of tracks (or bits of tracks) we ourselves have worked on and therefore know intimately what they should sound like and what problems we've had to address. The situation is more tricky for consumers, they don't know what/where/if there are problem areas and they don't know what any particular track should sound like. And again, usually we've got either a very good idea of what we're trying to detect (say from measurements) or a fairly good idea of what we're trying to detect. If for example we're comparing speakers, we might use a different set of test fragments/tracks than if we're comparing AD/DAs, because the artefacts are going to be significantly different.
Why would something at -100dB matter?
For the consumer, it wouldn't but professionally it could. Particularly with non-acoustic music genres (and TV/Film sound), raw recordings are very likely to be heavily processed and therefore some artefact at -100dB could end-up becoming audible. A consumer should never encounter this situation though, unless they have some pretty serious flaw with their setup (very poor gain staging for example) but then of course they should address that flaw, rather than looking to improve something that should be well below audibility.
G