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Line inputs: amplification on interface vs digital?
Old 1 week ago
  #1
Lives for gear
 
Line inputs: amplification on interface vs digital?

I used to just raise the gain knobs on my audio interfaces to amplify any line signal (mostly synths) to get a good volume in my DAW so I don't have to re-amplify it in my DAW. Usually I do bring the levels down again during mixdown in my DAW.

Now I got to think about it: what would be the best in terms of sound quality?

No amplification on the audio interface, but like 20 dB amplification digitally in my DAW, or the other way around?

Would there be any significant difference?

I did some short listening test, but couldn't hear a difference. But I didn't really do proper testing.

I would think that raising the amps on the audio interface could potentially color the sound, but I think that when you amplify digitally only, it might give you a higher noise floor? Or is that wrong?
Old 1 week ago
  #2
Lives for gear
 
🎧 15 years
This is kind of an odd question, but I think I understand it. Can you give more detail on what gear you are sending into your line ins?
Old 1 week ago
  #3
Gear Head
 
🎧 10 years
It's hard to hear stuff sometimes, because the equipment has relatively low noise floors and large usable ranges.

Unless something is set way wrong, you're not going to hear a lot of large changes to stuff from normal linear amplification. I mean, people tell me they hear it, but it's possible I am just old and can't hear the difference between a linear-functioning API preamp channel and a linear-functioning Neve channel.

Any how.

There are a lot of strategies and if you want to get nerdy about it the concept you'll want to google is "gain staging".

Plus some meters are telling you different things... they may be measuring different dB scales calibrated to different ideas of 0dB.

Any easy way to do stuff without thinking too much is to follow two simple rules:

- don't push anything into the red if it isn't designed to be pushed into the red or if it doesn't sound good. Mostly things aren't too critical unless stuff is overdriving things or if you're cranking up a very low signal

- if you are measuring the gain at the converter, shoot for around -14dB "Full Scale". There is a certain amount of thought that went into that, but that was a consensus by some folks I trust about what isn't going to overload the AD converters and still get maximum use out of the noise floor. I am sure in the 2 decades since I was taught that there have been additional ideas and discoveries, but it's served for a long time and the underlying arguments I'd assume are still sound

Here is an example.

So, like I have a korg sv-1, a yamaha mg12 mixer, and a focusrite scarlet interface, and I am working in Logic

- I set the keyboard volume to the middle of it's range
- I set the mixer gain to whatever lets me turn the channels fader about half way up
- I set the output of the mixer to somewhere in the middle of the master fader's throw
- I turn up the gain on the scarlet (or I turn down the output from the mixer) so that the meters inside it (which are dDFS) are peaking somewhere below -14dB full scale

The channel gain in Logic should match the input levels on the scarlet.

This results in a recording that is kind of low level-wise compared to, say, prerecorded samples or VSTs, and so I will often find myself using a compressor plugin with no ratio to up the gain on the channel, assuming that I am adding stuff in the box.
Old 1 week ago
  #4
Gear Head
Quote:
Originally Posted by MPrinsen ➡️
No amplification on the audio interface, but like 20 dB amplification digitally in my DAW, or the other way around?
Prefer to amplify in the analog domain. With modern stuff (i.e., not tubes), you won't color it so long as you're not clipping or near clipping (say... within 6 or even 3 dB). Op-amps and ADCs are really good at what they do.

Once you enter the digital domain, any low-level detail you've lost due to quantization is gone forever. Digital gain amplifies quantization noise and analog/signal noise, analog gain just amplifies the analog/signal noise.

Better still is to turn up the synths themselves, even if you have to engage a pad at the I/O interface to avoid clipping. You want to maximize the signal relative to any noise picked up along the analog path. Many synths naturally run "hot", i.e. at the highest levels most audio equipment is capable of; take advantage of this.

Of course, you really want to make sure that your synth at its loudest levels isn't clipping the audio interface's preamp, or ADC. Use the interface's pad switch (if it has one) to avoid preamp clipping, and the gain knob to back off from clipping the ADC. Triangle waves are good for testing this, as they have a high crest factor and are easy to see clipping or nonlinearities, despite that they sound quiet, but test also things like filter self-resonance and feedback. (Make sure of course your synth doesn't clip or color its own output at its highest levels.)

Beside experimentation, you can approach this mathematically. Many synthesizers specify (in dBu or dBV) the loudest output they are capable of; this is hard-limited by their internal power voltages (not necessarily their input voltage) so it is a safe guarantee. Most audio interfaces similarly specify the loudest input they can handle -- this is also governed by internal power voltages but also whether a pad switch is available -- and how much gain their preamps can provide. The difference in these numbers can tell you how by how many dB you need to cut your synth, or by how much dB you can raise or must lower the preamp gain. Just remember dBu and dBV are different; dBu measurements are higher by about 2.2 dB than dBV measurements (i.e., dBu is the "smaller" unit).

Moreover, because of the realities of voltages actually used in audio gear, most fall into one of two ranges, either "consumer" or "professional" (sometimes identified with "nominal" levels of -10 dBV and +4 dBu). These roughly correspond to "stuff with a unipolar +5 V power rail" and "stuff with bipolar +/-15 V power rails", and their maximum outputs are respectively limited as such. ("Consumer" stuff also usually has RCA jacks or 1/8" jacks; "professional" stuff 1/4"; but that's not a hard and fast rule.) So you can basically just figure out good settings for these two classes of gear and pick one or the other for any given synth.
Old 1 week ago
  #5
Lives for gear
 
🎧 10 years
This is part of gain staging. For every item in the chain, you decide who adds the gain based on how the finished signal sounds best. Does not matter that some of the chain is analog and some digital.
Old 1 week ago
  #6
Lives for gear
 
Ok thanks all. Apparently I have been doing it right after all just wanted to make sure
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