Recording input levels

...some further clues:

• If I turn down the input signal on my audio interface, I can 'shrink' the amplitude of the recorded waveform, but turning up the signal never get's it past the level shown in the pic above (although it does get a lot noisier!)
• I have opened the track in Logic, and turned off every plug-in and bus: same effect.

I'm wondering now if GB does some auto-compressing, or limiting, to prevent clipping. I can find no other source.

I also realise that the +/-100 vertical scale on the track editor is not dB, but I don't know what the scale actually is and can't find it in the manuals.

Thanks all,

D

Thank you both for your continued interest and support. Sorry I was slow responding but I was away for the weekend. So, in no particular order, my Record Level slider is greyed out, and set to zero - or all the way to the left. The Automatic Level Control checkbox is also greyed out and unchecked. I expected this for exactly the reason HangTim suggested, In fact, from the online Garageband Help:

"If the Recording Level slider is dimmed, you can’t change the input volume in GarageBand. In this case, use the device’s own volume control." That is what I do.

Where my confusion comes, is in the output of the Tascam. The clipped waveform I posted above is the waveform that appears even when the out is turned down to where the red overload light ("O/L") is not even flickering i.e. the signal is being clipped even at an output level below which the interface warns me of overload. If I ignore the red light and whack up the output level, it still appears to clip at the same level but the underlying signal is just way more noisy:

If I continue to turn it DOWN to below the levels above, I can get a clean and perfectly usable signal strength:

Obviously, I have however found some limit of the interface, or the cable, or my old USB2 port, that is causing this clipping at the 75% mark on the scale.

BREAKING NEWS: I have just discovered the source. My interface has a basic mixing capability: you can add a line/mic and a guitar, or two mics, then choose to have a mixed stereo output or two separate outputs for two separate inputs. I had the little switch set to stereo output. The mixer seems aware the only one input was live/plugged so it clearly shows a mono output, unlike the tell-tall dual waves of a stereo output. (The input source is also shown as mono in the dropdown). However, for research, I flicked the switch on the underside of the interface to dual outputs, played the same solo, and got this:

It would appear that I sacrifice gain or signal strength when the interface thinks it's mixing a stereo output. I guess that kinda makes sense, without knowing the actual output dB capability of the line. Anyway, it was definitely the Tascam, and I have definitely found a way to overcome it. And thanks to HangTime's earlier advice, I don't need to...

Thanks again all,

D

Ah. It’s your good self: you helped me before, thanks.

I am using a Tascam US-322. Electric guitar to interface, then interface to Mac via USB. I agree with your point about the signal looking clipped. The input signal dial (which is actually the output of the interface) on the Tascam has both a green and red light - the red indicating clipping, often on loud notes or chords for example. You then “dial back” the signal strength to where no red shows, thus varying it for different output pickups, for example. It’s a few years old now and might be limited itself in signal output strength on the guitar line, or the clipping indicator might be less-than-accurate, however it does seem odd that as I turn up and down the signal, it always falls and rises nicely but bumps into that +/-75% level.

Anyway, as you say - and I’ve learned something new - 50% is hot enough. So I won’t burn too many cycles on this given how much else I don’t know! Thanks again for your help.

D