My two (maybe more) cents here: Basically, it all comes down to signal/noise ratio of virtually any low-output sound, which purpose is to be *transformed after* (either by raising volume OR compressing OR converting to mp3 before uploading to wikiloops :) ). That is, probably, any recording we make as music producers :)
INTRO.
There are no "silent" audio path in the world, there are only paths with noise, low enough not to be noticed by human ear. Only systems that are turned off are silent (BTW considering the possible radio waves interference with metal parts of gear components, the last statement can be debated as well).
Disclaimer: I am NOT a professional audio engineer and I may be wrong. But that's how i see it:
I. Why
Due to low electrical output of the pickups and microphones, the signal should be amplified quite drastically to achieve what we actually hear on the record. To avoid increasing the noise level (inherent to any situation using outboard devices) along with the signal level, the signal better to be separated from the noise floor as much as possible (by increasing the signal evenly, but without increasing the noise) before any further processing to be made -- this way next gear in chain is working with louder audio and requires less input gain, reducing the added noise even more. That process is better done, as I understand, with electric processing than audio processing. And this is why DI should be first in chain.
II. Bass
Bass frequencies are usually (compared even to guitar!) harder to catch and transfer and thus pickups produce even lesser output signal. At the same time, due to small speakers through which music is consumed nowadays, PLUS the request for bass prevalence in contemporary culture (at the same time!) -- the small-output signal produced by bass pickups should be increased the biggest possible way from recording to mastering, compared to none other recorded instrument in the band. The lower (volume-wise) 'good' signal level is (very approximately represented by visual "wave height" in your DAW), the closer it is to the aforementioned noise floor -- and simple volume increase can make the noise audible quite fast. It can be pleasant sometimes, but once you start applying compression to bass, the high-frequency noise starts "pumping" very noticeably -- and that's very UNpleasant and hard to remove. Adding OverDrive or Distortion makes situation even worse.
III. Some cases when you don't need DI
Some devices act like DIs themselves or have DI built-in as an integral component, even if it is not stated explicitly. No need (no harm as well) to use the additional DI in front of those, unless your DI gives some coloration to the sound AND you're not overloading the inputs. Note that most of DIs have the "link" output, which transfers unchanged signal to such kinds of devices, like a bass Amp. Anyway, your creativity is the main priority and judging by your own (anyones' reading) ears should be the criteria.
SUMMARY:
Every audio processing unit provides better (clearer and richer, more musical) results if it receives loud signal, free of noise. DI should be put first in chain -- to reduce the unwanted processing of electrical noise by next processing unit(s). But, if it suits you musically, you can do anything! There are no rules, including this very rule about no rules. ;) Just record and mix with your ears, not with eyes!!! B)
Edited by
wishnewsky on May 18 2019 13:16