KVK: Where to start…lets work backwards from your most recent question:
“By running the pre-amp signal through the 1/4” TRS channels (only option from the pre-amp) the signal was limited to +/- 10 dB, while running the XLR through the mic inputs (Ch. 1 and 2) with NO pre-amp gives +14 - +55 dB!!!
I think that is my “signal attenuation” right there, yes?"
Not necessarily, that just means that the line inputs can go from 10dB attenuation (signal reduction), to 10dB gain (signal amplification). That is in addition to whatever amplification that the Vintech preamp provides. So what did you have the line input gain set to when you had the Vintech preamp connected? You said you had the Vintech set to the -35dB sensitivity setting, but I can’t tell what that is referenced to. I guess depending on whether that means that a -35dB input is amplified to 0dB or +4dB (standard line up level) that could mean that the Vintech had 35dB to 39dB of gain. Then plus or minus whatever the FP10 control was set to.
Hopefully you can clarify what you meant with some of your earlier comments. I can’t tell if you still don’t understand the gain structure, or if you just aren’t familiar with the standard terms.
“signal chain: mic - XLR - FP10 - firewire - Ardour”
How are you judging the noise levels? Headphones, or speakers? If headphones, from the built in headphone amplifier, or an external? If speakers are you using the main out or the cue out?
“FP10 outputs set to unity (straight up middle),”
By outputs do you mean inputs, and by unity do you mean not unity? From what I can see in the manual, there are preamp input gain controls, but no controls on the outputs. And you say unity, which would be 0dB, but the gain range settings of the preamp inputs are 14dB to 54dB. Are you perhaps reading the scale for the line inputs, which have a range of -10dB to 10dB? I can’t make out the front panel text in the PDF manual, but I would guess that when the knob indicator is straight up that would be about 30dB or 35dB gain.
“track/bus/Master bus meters set to -25 dB FS”
By set, you mean that is what you get in the meters when the gain knob is straight up? Using what as a signal? Just strumming a guitar, or something like that? -25dB is really low, you are giving up quite a bit of dynamic range right there.
What are you changing in these setups where you describe the input gain setting as the same, but the signal level shown in ardour is different by 10dB?
“5. KSM mic, phantom power, Channel 1 FP10, FP10 outputs set to unity (straight up middle), track/bus/Master bus meters set to -25 dB FS
6. KSM mic, phantom power, Channel 1 FP10, FP10 outputs set to unity (straight up middle), track/bus/Master bus meters set to -15 dB FS”
What changed that made the signal go from -25dB FS to -15dB FS?
“a. It’s perfectly fine to set the FP10 output gain near max;”
It’s input gain, but ignoring that, of course it’s fine to set the gain near max if you need that much gain, that is why there is a control knob.
More detail: Every analog to digital converter has a maximum input level it can take, if the signal is amplified such that the peaks of the signal would be above that maximum input level, the peaks are “chopped off” and you get nasty distortion.
That sets the maximum gain you would use with a particular microphone/instrument combination. You obviously would use less gain with something loud like drums, and could use more gain with something quiet like finger style nylon string guitar.
At the other end of the signal range, the converter has an intrinsic amount of noise that sets the noise floor, so you want enough signal level that the signal can be heard clearly, but without distorting, and such that the noise floor is enough lower than the signal level it is not annoying.
Not only the converter has intrinsic noise, the microphone amplifying circuitry, the impedance buffers in the phantom powered microphone, even the microphone cartridge itself has intrinsic noise due to the air molecules bouncing around.
So the balancing act is you want to amplify the microphone signal at least enough that the noise level of the microphone itself becomes slightly higher than the noise level of the microphone preamplifier and A/D converter together. Any higher gain after that and you are just amplifying the noise more, once you hit that point you can increase the level in the digital editor. To a large extent that is a problem for the designer of the preamp/A/D converter combination to work out, mostly what you need to keep in mind is that if you turn up the gain too high you might distort, but if you keep the gain too low there will not be enough separation between the level of the signal and the level of the noise.
“It’s perfectly fine to record with the track/bus meters set anywhere between -15 and -5 dB FS”
Yes, that would be my recommendation.
“Channels 1 and 2 are the only appropriate ones for direct XLR mic input”
Read the manual again. Don’t know how on earth you came to that conclusion, channels 1-8 are identical from the XLR inputs. Section 3.1, “Your FIREPOD is equipped with eight…microphone preamplifiers”
“the Vintech isn’t really necessary (??)”
Definitely true. The Vintech should be used if you like the particular sound that Neve-style pre-amps have when you push them really hard.
“and in fact MAY be part of the responsible party for all my hiss crap”
Noise is additive, so to the extent you add additional unneeded devices, you will be adding more noise. Whether that is a net improvement or net detriment depends on what the device does and how it does it. But in this case, if you want to just amplify the microphone signal and not use the preamp as a signal processor to add a particular flavor of distortion, yeah, probably more harm than benefit.
“Now - I am curious why I still needed an amplifier plug in set to 5-6 to reach -10dB output on the bus meter when the FP10 gain was set to max - 8 clicks (sorry - no idea how better to describe it!) and the track/bus meters all set to -10dB.”
Not enough info to understand what you are describing. First, is the meter type set to the same on both the tracks and the master bus? You can select different styles of display, and I don’t remember what the default is on the 3.5.x builds.
The connections from tracks to busses in Ardour do not have any attenuation, so if a signal peaks at -10 dB on the track meter, it will peak to -10 dB on the bus meter if the track fader is set to unity (0dB), the bus fader is set to unity, and the meter style is identical for the track and bus.
And of course as you mix multiple tracks together, the peak output on the master bus could be higher than any individual track if the tracks have sound occuring at the same time (the typical case).
" to what are you referring when you say “mix control all the way to input” (FP10 output to near max??), and channel gain control (I’ve been calling this the track/bus peak meter?)."
The channel gain control, or the input gain control, is actually I think what you have been calling the output gain control. It is controlled by the set of 8 knobs just to the right of the XLR connectors, 1 knob for the input gain of each channel. It is what the FP10 manual calls the input gain/trim controls (see page 15).
To the right of those knobs are three additional knobs. The knob labeled “main” is a volume control for the main CR outputs on the rear of the firepod. That is so you can set how loud your speakers are playing independently of the signal level shown on the bus meters. Alternatively you could use an amplifier with a volume control built in, or an external preamp/volume control type of device to your amplifier or powered speakers, assuming you are using speakers.
The knob labeled “phones” is the volume control knob for the headphones. Like the Main knob, but changes the headphone amplifier level instead of the Main CR Output level.
The Cue Mix output, the Main CR Output, and the headphones output are a mix of the channel 1 and 2 outputs, and all 8 inputs, with the balance between the channel 1 and 2 outputs, and the sum of all 8 inputs controlled by the Mix knob. All the way to the “playback” side and you only hear what your audio program is sending to outputs 1 and 2, all the way to the “input” side and you only hear what is coming in on the inputs, nothing being played back from the computer. That is so you can monitor an overdub without having to worry about any delay added by going through the A/D converter, through Firewire to the computer, through the audio program routing, back through the firewire system, and out the D/A converter.
That could be relevant if you are using the headphone amplifier in the FP10 to check the noise level, because the setting of the Mix knob will determine whether you are listening just to the outputs coming from the computer, or also to the sum of channels 1-8. Especially if you didn’t pay attention to the gain knob setting for the channels you weren’t using, you could have a lot of extra noise being added to the headphone output.