firepod converters calibrated to?

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djclueveli

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does anyone know what the presonus firepod converters are calibrated to? also does it matter what xlr cords u use?
 
Presonus does not publish that spec for the Firepod. What you can do is set all input and output gain control on the Firepod to unity (zero gain), and set the input fader in your DAW software at unity gain. Then generate a 1kHz sine wave tone with a synth or tone generator and play it into the line in of the Firepod at 0VU/+4dBu. Read the reading on DAW meters, and that should then tell you the conversion rate.

G.
 
I used the virtual MR1 on the RealTraps site to generate a sine wave at 1khz at +4dbu, plugged my soundcard's line out into my firepod's line in, and Sonar reads it at -24.2db. At 0dbV, it's at -26.2db peak. Into the inputs on the front, it's a different story. -10.4db at +4dbu, -12.4db at 0dbV.

I dunno what I'm doing...Help me here...But the average of those numbers is -18.3.

Would that mean that -18db is a good estimate to shoot for or am I wrong and is -10 or so where it's at? I've been recording things at -18db peak in Sonar for months now and it'd suck if I'd be getting better results at -10db.
 
mrhotapples said:
I used the virtual MR1 on the RealTraps site to generate a sine wave at 1khz at +4dbu, plugged my soundcard's line out into my firepod's line in, and Sonar reads it at -24.2db. At 0dbV, it's at -26.2db peak. Into the inputs on the front, it's a different story. -10.4db at +4dbu, -12.4db at 0dbV.

I dunno what I'm doing...Help me here...But the average of those numbers is -18.3.

Would that mean that -18db is a good estimate to shoot for or am I wrong and is -10 or so where it's at? I've been recording things at -18db peak in Sonar for months now and it'd suck if I'd be getting better results at -10db.
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Assuming your soundcard is truely delivering +4dBu to the FP (can you verify that?) and there is no boost or cut of the signal somewhere along the way (esp. on the FP itself), then it sounds like it's calibrated for 0VU/+4dBu = -24dBFS.

That front reading sounds like it's going into a mic pre, in which case you're reading a falsely amplified level. And the average between the two readings is just coincidental, I believe, and has no real meaning.

That -24dBFS number, while not at all unreasonable (tons of peak headroom! ;) ), does seem just a taste low from what I'd expect. I'm wondering if perhaps your soundcard is actually sending -10dBV into the FP instead of +4dBU? If so, then that would probably mean that you're actually equating line level to about -12dBFS, which is just a taste on the high side, but does sound a bit more "European" in design convention.

In summary, at face value you're telling us that your FP is calibrated for Line Level = -24dBFS, but I'd like to verify that all your testing ducks are actually in a row.

G.
 
How would I go about getting an accurate reading then? I've got the volume controls all the way up in Windows. The sound is louder when going through the Firepod's preamps, but the direct line in is -24dbfs to -22dbfs. I'll do a test on another computer with a different soundcard under the same settings. If this is true though, then I've been wasting 6 decibels of headroom.

And that sure is cool, that -18.3 thing, I love coincidences!
 
mrhotapples said:
How would I go about getting an accurate reading then? I've got the volume controls all the way up in Windows. The sound is louder when going through the Firepod's preamps, but the direct line in is -24dbfs to -22dbfs. I'll do a test on another computer with a different soundcard under the same settings. If this is true though, then I've been wasting 6 decibels of headroom.

And that sure is cool, that -18.3 thing, I love coincidences!
Click to expand...
Well, some coincidences are really not all that surrendipitous ;). Notice that the two possibilities I gave you (-24dBFS and -12dBFS) also happen to average out to exactly -18dBFS. Also a coincidence? Not really. There is nothing "magical" about the -18dBFS number, other than the fact that it's often quoted exactly because it is a fairly average calibration setting.

If you're unsure about your sound card's specs (they can often, but not always, be found on the Internet), the the question would be if there's anything else in your signal chain before the Firepod that does have VU meters calibrated to +4dBu line level.

For example, if you have a mixer with VU output meters, what you could do is record your sine wave to casette or reel tape. Then play back that tape through the tape ins on your mixer, and set the master bus faders to register 0VU on your output meters and run your main outs to the FP. The quality of the recorded signal is not so important for this test; it's the constant, calibrated level that's important.

Another alternative if you have an external mic pre with a calibrated VU meter available would be to play the sine through a loudspeaker. Mic the loudspeaker through that seperate pre and set the output level to 0VU. Then run the line outs form the pre into the line ins on the FP.

Again, with any of these tests it's important to have the gains on the FP set to unity gain (no boost/no cut) so that you're running a true 0VU line in to the FP and so that the converted signal coming out of the FP is also not boosted or cut going into the computer.

G.
 
I have a 3630...I plugged my soundcard into it, no gain, no nothin'...It read -2dbfs at +4DBU. Sonar still read -24dbfs at the line in. Since I'm actually getting -2dbu from my soundcard, this means that Firepods are calibrated at -18dbfs!

Right?
 
mrhotapples said:
I have a 3630...I plugged my soundcard into it, no gain, no nothin'...It read -2dbfs at +4DBU.
Click to expand...
I assume you'e talking about an Alesis 3630 comp? And I also assume you meant to say -2dBVU instead of -2dBFS?
mrhotapples said:
Sonar still read -24dbfs at the line in. Since I'm actually getting -2dbu from my soundcard, this means that Firepods are calibrated at -18dbfs!

Right?
Click to expand...
That could be true, assuming that the reading you took on the 3630 was with the meters set to output level and not input level and that you did indeed mean an output reading of -2dBVU on the 3630 (and assuming that at range that 1dBVU is going to yield about 3dBFS, which is *normally* correct.)

I'd still like to see a verification with the output metering on the 3630 set to exactly 0VU, using the output gain on the 3630 to bring the level up those couple of dB, just to be sure we're comparing apples to apples here.

G.
 
i'm so lost with this dbfs stuff and line signal. i dont use my sound card. i just plug my firepod into the firewire and use that as my sound card. and when people say -18dbfs is that depending how loud u sing or not or its just a certain amount of gain of the firepod or whatever other gear using it. so if i wanted to get a whisper sound to -18dbfs does that mean i have to crank up the gain all the way so my voice will reach as high as -18dbfs? i'm so lost. so glen or anyone else do u mind eplain this again one more time lol. and also to see the dbfs in soundforge to i go to tools and then statistics and the read the RMS level? also mrhotapples how come u dont just use the firepodwithout pluggin it in to the soundcard? doesnt the firepod have better sound than the soundcard? i have a sound blaster sound card. also to what oclock do u normally turn the gain to get a good vocal take. thanks
 
This is all so confusing...If my 3630 is calibrated to +4dbu, and I send signal from my soundcard in, and it reaches -2db on the input meter, do I not assume that if I add 6db, it's at +4 and that if Sonar picks it up as -24db, adding 6 to that makes -18 to compensate for my sound card outputting too low a signal?

I dunno. Confusing!

But...Gain is bad...I don't like it. I never use gain for snares and overheads (NEVER for overheads) or toms 'cause they always peak around -18db when I'm recording them. If they're significantly quieter, I turn them up a little. Vocals are different. If I sing into a mic 6 inches away, it's peaking -15db. I'm loud. Some screamers I record are loud enough to get to -9db in spurts, and some singers so quiet that I need to turn the gain half way up. I have never, ever in the 8 months I've had it had to use all the gain.

I will, for now, continue to to record at -18db for my loudest signal, because it hasn't failed me yet. It's somewhere around there anyway!
 
djclueveli said:
i'm so lost with this dbfs stuff and line signal. i dont use my sound card. i just plug my firepod into the firewire and use that as my sound card. and when people say -18dbfs is that depending how loud u sing or not or its just a certain amount of gain of the firepod or whatever other gear using it. so if i wanted to get a whisper sound to -18dbfs does that mean i have to crank up the gain all the way so my voice will reach as high as -18dbfs? i'm so lost. so glen or anyone else do u mind eplain this again one more time lol. and also to see the dbfs in soundforge to i go to tools and then statistics and the read the RMS level? also mrhotapples how come u dont just use the firepodwithout pluggin it in to the soundcard? doesnt the firepod have better sound than the soundcard? i have a sound blaster sound card. also to what oclock do u normally turn the gain to get a good vocal take. thanks
Click to expand...
The only reason he's using the soundcard (I believe) is as a way to generate the test tone signal he is using to test calibration on the FirePod. In other words, he's just sending a sine wave out of his sound card so that he can send that sine wave into the FirePod to see what kind of levels he gets through the FirePod. Otherwise, the soundcard is not normally part of the recording process.

As for the rest, it's all about "gain structure"; which is a fancy term meaning "making sure you have your signal levels set properly at every link in your recording chain".

Where peopley mostly get confused is in how the conversion from analog to digital affects the signal level measurements, how dBu, dBVU, dBV and dBFS are all different animals measuring the signal in different ways, and how the calibration on the converter affects the exchange rate between the different types of dB measurements.

It's all too long of a topic for a single forum post. I do have an interactive chart on the whole topic due out in the coming weeks; in the meantime I suggest you do some searching on "gain structure" and "gain staging" to get more info.

As far as the whispered vocal, this is where gain structure can really get important. the key to a quality result there is *where* you do the signal boosting to bring the whisper up to audible levels. Do you do it all in the preamp? Do you just boost the track in your DAW software? Do you push the signal going into the conferter? There is no one right answer to that. While most of the boost is probably usually done at the preamp, sometimes how much is done there it depends entirely on the quality of the voice and the quality of the gear at every point in the signal chain. Knowing your gear at each stage and understanding how to balance your gain structure throughout the input chain will tell you how much to do at the preap, how much to do as makeup gain in a compressor, how much to do in mixing, etc.

G.
 
mrhotapples said:
This is all so confusing...If my 3630 is calibrated to +4dbu, and I send signal from my soundcard in, and it reaches -2db on the input meter, do I not assume that if I add 6db, it's at +4 and that if Sonar picks it up as -24db, adding 6 to that makes -18 to compensate for my sound card outputting too low a signal?
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Nope.

This is exactly what I mean by knowing the difference between the different type of dB measurements. dBu is not the same as the dB readings on your VU meter, and neither of those are the same as the dBFS readings on your Sonar meters.

dBu
+4dBu is nothing more (at this level) than a way of saying "line level voltage" (0.775volts). This is the average signal level your analog hardware and cabling is designed to optimally operate around.

VU / dBVU
The VU meters on your analog gear like your 3630 are calibrated so that 0VU equals +4dBu. that's why many VU meters change color at 0VU, black or green bottom 2/3rds below 0VU means a signal slightly below pure, perfect line voltage, and the red above means you're running slightly higher than standard line voltage. Of course the meters will be juming all over the place when recording; this is normal. As long as you keep the average level somehere around 0VU and don't let them go too crazy either way, you know you're somhere around normal design operating range.

dBV
This is not the same as either dBu or dBVU. It's a different way of measuring voltage than dBu is, and for the prosumer and pro gear that most of us use in this forum, it's a rarely used measurement.

dBFS
This is how things are measured on the digital side of the equation, after the A/D conversion. Here, 0dBFS means the maximum signal that your digital gear can put out. and is usually over a dozen or more dBs higher than line level (measured as 0VU/+4dBu.) Just what dBFS value equates to line level depends on the calibration of your A/D converter, which is exactly what we're trying to measure here.

To Recap
What you need to do is send a 0VU signal into the line in of your firepod. It's as simple as that. If there are no gain changes made in the Firepod or in Sonar (all knobs and sliders set to zero boost/cut), the meters in Sonar will tell you in dBFS how strong a line level signal is. No math. Just run a normal 0VU/+4dBu signal into the Firepod and see what comes out in Sonar.

Once again, you need to do two things on the 3630 for this test; you need to make sure your meters are set to output and not to input (they are switchable, I believe). This will tell us exactly what is coming out of the 3630, and therefore exactly what is going into the Firepod. If the sine wave signal from your soundcard is too high or too low (above or below 0VU), use the output gain control on the 3630 to adjust that output level until it's reading 0VU.

Get all of the test recap details right and your Sonar meters will tell you straight out what your Firepod A/D calibration is.

G.
 
thanx alot glen for that post. i will definetly do some research on it. mrhotapples u only turn your gain up to halfways sometime? for me doin a regular vocal take i have to turn my gain to a little over 3 oclock. im loud but not screaming like u said. isnt 3 oclock to high? i hope my firepod or mic is not messed up. can that be possible? and when u say u peak at -9db do u mean on a peak meter?
 
I mean in Sonar. And it all depends on the mic. And your defenition of loud...I can sing loud enough to be barely audible aboved a drum kit. Through a sensitive condenser, I never (okay, hardly ever) have to use gain.
 
yea but what im sayin is that if i dont turn it up to 3 oclock it barely pick up any signal and i have a shure ksm27 condenser mic. sonar peak meter right? theres different measuring meters. so when u turn the gain on the channel all the way down u still pick up a good signal or do u have to loud it by like 20 db cause turning the gain on the preamp all the way down means that u will piick up almost nothing. please be specific
 
I just tried this out for you, to make sure I am right about my own bag. Speaking volume at half gain on the FP with a CAD m177 6 inches away, I peak -18db. Singing I'd probably be at around -15 easily. Without any gain, 6 inches away, I'm at -38db. singing I'd be at about -35 or so.

So I guess I overshot...But yeah, if you have to turn your gain up to 3 o clock to get usable vocals, the mic cable might be damaged, or you might be getting some quiet singers. At 3 o clock, I have to put the mic about a foot away and sing quietly.

So yeah, I don't know what the characteristics of your mic are, but you are not getting anything similar to me...And I'm using a 170 dollar mic. Something is wrong dude.
 
mrhotapples i tried it the way u did it but came out with much different results. when i turned my gain all the way down and spoke at speaking level i peaked at -53 db in my sounforge meter and when i sang i peaked at about -51.5. and the waveform is invisible until u increase the volume by 20db. i dont know whats wrong. i tried to raise it half way like u said and singin i peaked at about -31. i use a shure ksm27. What do u suggest is wrong? u think its the firepod?
 
It might be me or it might be you, honestly. I might have a broken unit, the main level has never done anything, and I got mine used. Try turning the main volume all the way up and THEN turning up the individual channel halfway and see if you get my results. This'll help us both out!
 
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