Questions about signal ratio, audio interfaces and garageband...

J

Jack of Alderaan

New member
Until recently i was using Garageband on an old mac with a line input so i used to plug the mic into a mixer, use its preamp then straight into the laptop. I could adjust the level both with the mixer and also Garageband's input level.

Last month i was able to get myself a brand new laptop and a proper audio interface. So now i have a macbook air m1 and a SSL2. I was trying to record some drums the other day with an AKG C214, the levels were good on the SSL2, hitting between -20/-10db on the interface if my memory is correct (only the max green lights, no yellow or orange). But on Garageband the soundwave looks a bit small, like taking a bit less of half the space before it clips. So without thinking too much about it i tried to increase the input recording level on the DAW only to find out that now it's greyed out and i cant use it....

From what i've read it seems that this is normal and i can only adjust levels with the interface, not the computer. Is this correct? Which leads me to another question: so how do i adjust the level now? I could slightly turn up gain on the SSL2 so it hits the yellow spot but i don't think it's gonna make a big difference and i run the risk of overloading. Perhaps i shouldnt think in terms of signal/noise ratio because it's digital? Maybe the soundwave is fine and i shouldnt worry about its amplitude in the DAW since this is not analog? And just use comp then manually turn up the track volume in Garageband if necessary?
 
You don't need a big (visually) wave form. You should be able to drag the tracks larger to make the waveform bigger, but who cares, unless you are editing by look.
 
This is quite normal on cubase and you can adjust a small slider to change how it looks - this doesn't change the actual level, just how it appears as a waveform. Does yours have the same function?
 
Oh i don't mind how it looks visually. My eyes dont really need it. It's more about the level of the recording being optimal or not. The mantra has always been "push the level as hard as you can" but maybe it's not relevant when you record in digital? I know it matters when you do that in analog, because of the noise floor you want to have your signal as high as you can. A good analog signal is a strong signal. But perhaps 24bit digital recording is more forgiving about this?
 
Jack of Alderaan said:
Oh i don't mind how it looks visually. My eyes dont really need it. It's more about the level of the recording being optimal or not. The mantra has always been "push the level as hard as you can" but maybe it's not relevant when you record in digital? I know it matters when you do that in analog, because of the noise floor you want to have your signal as high as you can. A good analog signal is a strong signal. But perhaps 24bit digital recording is more forgiving about this?
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MUCH more forgiving, so much so in fact that you comfortably record at -30dBFS and still have as good a S/N ratio as the analogue stages, mic, mic pre amp in AI etc, allows although folks generally find an average of -20dBFS with peaks no higher than -8 or so fine for most recordings.

Dave.
 
Jack of Alderaan said:
Oh i don't mind how it looks visually. My eyes dont really need it. It's more about the level of the recording being optimal or not. The mantra has always been "push the level as hard as you can" but maybe it's not relevant when you record in digital? I know it matters when you do that in analog, because of the noise floor you want to have your signal as high as you can. A good analog signal is a strong signal. But perhaps 24bit digital recording is more forgiving about this?
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That was the mantra back in the tape days, when much of the equipment might have 60-80dB of S/N max. Hitting +5 on a peak would introduce a little distortion and compress a bit, but it wasn't a horrible deal.

With digital, you probably have in excess of 100dB S/N with your equipment, so hitting -20 still leaves you 80 to play with. You absolutely don't want to hit 0 on the recorded signal, as anything above 0 simply doesn't exist! With 16 bit audio, you have 65536 discrete levels which represents a max 96dB S/N. 65537 is basically undefined, so you can't have it. Record in 24 bit audio and you have 16777216 discrete levels. This represents about 144dB potential S/N, which is generally in excess of 99+% of the actual equipment.

Most likely the limiting factor in your ultimate S/N is going to be your room!
 
Just to add a bit here, your input levels on the interface/preamp, you do want to have adequate signal going in. With any preamp, the theory is that you do want the most signal in for the preamp before clipping and distortion. If you are increasing the gain of a weak preamp to compensate for a weak input, then you will likely have more noise that you have to deal with. That being said, there is never a good of clipping basically anything at the preamp stage, unless distortion is your goal.

Never EVER do you want to be above digital clip level in a DAW. Should not ever even be close. That can be a struggle to get through the head if coming from analog recording. Wrapping your head around -18dbfs average is hard to do, but that is basically hitting the optimum levels in the digital realm. Even most plug-ins are designed to work best in this range. Now that kind of changes with plugins for drums and such that have transients upwards of -6dbfs, but your ears will tell you what is going on there.

And don't forget, dbfs in a DAW is not anything near the same as analog db. They are two absolutely/completely different scales of metering.
 
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"Most likely the limiting factor in your ultimate S/N is going to be your room!" Says Rich and this is almost always the case and with much lesser gear than an AKG 214 and an SSL2!

Mic first: this has a self noise of 13dB and whilst that spec is not of THE quietest mic on the planet it is some 3dB better than many LDCs and around 7dB better than most SDCs. It also has a very healthy output of 20mV/Pa. In short, nowhere short of a pro studio is going to be quieter than that mic! In fact on drums I am surprised the mic did not push the AI close to clipping? Many a very decent unit WOULD clip. The mic also has a 20dB pad. You don't have that engaged by mistake mayhap?

So, the interface. VERY good indeed! In fact HAD the SSL2 + sported two more line inputs I might have gone for it instead of my MOTU M4. The two interfaces are however very similar in their specifications i.e. close to state of art.

I do not know Garageband but no other DAW I have ever used has 'gain' controls on the inputs and I would aver peeps find DAWs hard enough to learn without THAT complication!

Dave.
 
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