What's the relationship between Hardware Gain control

What is the relationship between the hardware Gain Controller - the little slide wheel that can increase-decrease gain on the iRig Pro, and the actual quality of the recording?
The Gain controller on the iRig Pre, the little thumb wheel, has no scale or markings, so it’s pretty much guess work where it’s set. However, I normally just leave it running at the full setting… but I’m thinking that maybe I should turn it down a bit, in an attempt to limit the noise that the mic will otherwise “hear”, or make. Although visually it seems to make little difference other than to reduce the overall Volume of the piece?
What would be nice is a really large VU meter like Pro Tools First has, which shows me clearly what levels I am looking at.

This is not a major issue I have, I’m more curious about what Gain is and how it works - without being too technical. I have as good as got it right for Audible now, ACX, but will always fiddle to get it “just right”.

All microphones / pre-amps produce some amount of “noise” (hum, buzz, hiss). If the hardware gain level is low, then the audio signal will be low, so there will be proportionally more noise compared to the audio signal level. Ideally you want to get the audio signal much higher than the background noise level, so that means turning the recording level up. If the hardware gain is too high, then the signal will “clip” (distortion) which sounds like a horrible crunchy static noise when the audio goes loud. Also, some pre-amps produce a lot more noise when the gain is turned up to maximum so may work better (less noise) when set a little below maximum.

The short answer is, turn it up high, but not too high.

The meters in Audacity may be dragged to the full width of the computer screen. Audacity Manual

Give what you’ve told us about your setup and Mic, I would say "Yes just leave the knob on the iRig turned all the way up. I wouldn’t turn it down unless you see or hear clipping in the result, which is unlikely if you are just recording speech.

All microphones / pre-amps produce some amount of “noise” (hum, buzz, hiss).

Hiss, yes. Hum and buzz, no. Hum and buzz are environment problems and you can help that with shielding, positioning, eliminating buzzy lights, etc. etc. Hiss is atomic level and it’s burned into the MicPre. No amount of shielding, positioning, etc. is going to help. You are required to get the sound loud enough and arrange the MicPre adjustments so the show is A Lot Louder than the hiss. This is also the magic place that determines the noise floor forever. Absent Noise Reduction, the noise will never be any better than it is leaving the MicPre.

And that brings us to pushing MicPre design in the ads.

Onboard, you’ll find one of Behringer’s acclaimed XENYX microphone preamps

That’s from the UM2 ad.

In the other posting when you commented that the noise level was really high, I thought you were using the much higher quality commercial MicPre and that would have been very unusual (as I posted in my sample). It’s probably perfectly normal for an iRig.

Koz

iRig mic pre specs don’t look too bad:

Frequency response: from 20 Hz to 20 kHz +/- 1.5dB
Noise: -98 dB fullband, phantom power ON
Maximum output level: 2 Vrms
Distortion: 0.025% THD
Phantom max current: 6mA
Battery duration (Alkaline 9V cell): approx 30 hours when phantom is off, approx 10 hours when phantom is on

Noise: -98 dB…

The Shure 55s is a Dynamic (moving coil) microphone and has no noise of its own. Where did -54 dB observed noise come from? Worse, apparently base noise, before you turn anything else on. I can do better than that with everything running in a quiet room and holding my breath.

Koz

Where did -54 dB observed noise come from?

From the laptop’s line input?

Oh, right. [smacking head] It’s not a USB adapter.
Koz

Firstly, thanks guys. It’s all becoming clear. Much appreciated.
And the resizing of the meter… What do I tell others? … RTFM… I know I know … It’s a thick forest with lots of trees. Excellent.

So I looked into the iRig and the noise floor the last few days. The people from the company, tech support tell me that with the iRig plugged into the Mac, it’s always going to be noisier than if plugged into an iPhone/iPad - because it’s designed for the IOS side of things, not so much for the Mac/OSX.
However, it’s not real bad, and as I get the room quieter things get better.
Now I have a LARGE vu meter on the side, running vertically, I have the iRig on, the Gain turned now … hmmm, about one full wheel rotation, and the mic is OFF. The meter is fluctuating - bouncing - between -64dB and -67dB.
With the Gain up full it’s bouncing between about -57 and -62. So the iRig itself is generating noise. It’s of course plugged into the Earphone socket of the Mac Mini, which also acts as the mic input. It’s the way the iRig is made. No matter, I can get good sound out of it, and have already passed the Sample test with Audible, in that respect. Not the room noise etc, but the peaks and floor etc that ACXCheck looks for. Keeping the Gain adjustment turned down a bit.

However, I’m buying one of these next week - So hopefully a lot of other problems will go away. It does USB. I’d also like to be able to plug it into the Line In port on the Mac Mini as an alternative, but can’t figure if it will do it or not.

I now have real good (Numark) headphones - and big surprise, I can hear noises I didn’t think were in there… This is an interesting exercise.

Thanks for the help folks.

By “gain” are you referring to the knob on the iRig itself, or to the gain control from within Audacity (which is controlling the electronic gain on your mic input)? If the former then your conclusion is correct, if the latter, then the noise may well be coming from the input stages of the Mac’s microphone amp.

Yes you will have that option, you will need a cable that goes from the Phono jacks on the back of Scarlett to the mini-phone jack on the Mac, and turn on the “direct monitor” switch. That said, I would say that it is very likely that the A/D conversion within the Scarlett will give better results that the converter in your Mac. The main thing to watch out for (and impossible to predict) is the appearance of 1kHz USB data whine in the audio (what Koz refers to as frying mosquitoes).

Yes I find headphones to be the best listening tool for QC’ing a recording.

-Will.

Congratulations! You’ve done your first real-world noise floor measurement. That’s the value I’d expect from your preamp, combined with environment.

With the Gain up full it’s bouncing between about -57 and -62. So the iRig itself is generating noise. It’s of course plugged into the Earphone socket of the Mac Mini, which also acts as the mic input. It’s the way the iRig is made. No matter, I can get good sound out of it, and have already passed the Sample test with Audible, in that respect. Not the room noise etc, but the peaks and floor etc that ACXCheck looks for. Keeping the Gain adjustment turned down a bit.

It is wat is to be expected from a preamp in this class. At 100% gain, they’re all a bit noisy. You have to spend serious dollars to get significantly better preamps.

I’d also like to be able to plug it into the Line In port on the Mac Mini as an alternative, but can’t figure if it will do it or not.

I don’t think you can go from the output of the Focusrite interface to the line in. But i’m not sure I understand what you want to do.

Connect to the line-in while connected via USB to another computer?

If you mean using USB and the line-in on the same computer, what would be the use? You can record over USB, what would the line-in connection add?

If you mean using USB and the line-in on the same computer, what would be the use? You can record over USB, what would the line-in connection add?

sorry, no, one or the other. not at the same time.
I want to discover which gives the bettet quality, USB or line in.
thanks.

That’s easy.

Only USB is simple to work with and will give you the best result.

Using the built-in, zero-latency monitoring of the Focusrite won’t work, as this is a mono signal.

And using the FR’s outputs to go back into the Mac mini’s line-in will work, with a lot of latency and will give a slightly lesser quality. The signal has to pass through the ADC, via USB into the computer and back out via the DAC into the line-in.

However, there’s no sense in the last setup as the FR needs to be connected to USB for power and control. It’s not able to operate in “stand-alone” mode.

Ah, I see. of course. USB power… Ok, that clears that up. Anyway, the FR is on it’s way, and will do what I want. What I will do over the next little while is find something that doe3s go into the Line-in port directly, and experiment with that.
Meantime, I have to get on with recording if I am ever to push this project forward :slight_smile:

Thanks for the good advice. Much appreciated.

Don’t forget the line in on the Mac is also an optical digital in. The biggest advantage over the analog line-in is that it is completely electrically isolated because it’s optical.

Unfortunately, preamps with optical out tend to be expensive and rare. Examples:

https://proaudio.com/catalog/art-dmpaii-2-channel-mic-preamp-with-digital-outputs.asp
http://audient.com/products/mico-dual-microphone-preamplifier
http://www.gracedesign.com/products/V3/V3frame.htm
http://crookwood.com/audio-recording/paintpot-mic-preamp/
http://www.sweetwater.com/store/detail/Channel
https://www.gbase.com/gear/universal-audio-la-610-mkii
http://www.core-sound.com/Mic2496/1.php
http://www.bhphotovideo.com/c/product/406896-REG/Denecke_AD_20_AD_20_Portable_Microphone_Preamp.html

You can use it as an optical digital out too, going fi into a surround receiver and playing 5.1 surround sound.