Studio monitor "hiss"

[CochraneDrumTutor]

Hi
(Warning! another "newbie" question incoming )
So I have the following set up: Zoom L20 Mixer https://zoomcorp.com/en/us/digital-mixe ... trak-l-20/Adam T8V Monitors https://www.adam-audio.com/en/t-series/t8v/ and a range of Audix mics on an acoustic drum kit. No other links in the audio chain so to speak.

I have been working to "gain stage" the drum sound and have something I feel it pretty balanced and that doesn't "clip" even when all the mics are recording. (It's nudging @ -5Db)

When I play a recording back out of the speakers (all channels set to 0Db including the Master output) I get a decent clean sound BUT I was getting @ 60Db reading on my phone app, and I had heard people say a good level to listen to Studio monitors is @ 80Db (and honestly I wanted a it more volume too)

So rather than alter any of my carefully constructed "gain levels", I altered the Db levels on the backs of the speakers, so that I got more oomph and something approaching 80D from them.

What I then noticed was that with all the faders set to 0Db including the Master fader I hear a hiss from the speakers.
BUT...
IF I pull all the faders down to - infinity (except the Master) the hiss goes.
Also...
If I play some properly recorded music (in this case the Wonderful Alison Krauss and Robert Plant's new album which I'd highly recommend btw) at loud volume (with all other channels at zero) I get NO hiss.
BUT
If I slide the faders of the channels back to 0 the hiss returns..

So, (finally!) I get to the questions:
What might the root causes of this?
What is the best way to get the levels from the kit I want plus good output levels (@ 80Db) from the speakers without hiss creeping in?

I do hope that all makes some sense?, and many thanks for any thoughts you might have on this type of issue?

[Philbo King]

It appears to be mixer noise, since it varies with fader level.

[ef37a]

"BUT...
IF I pull all the faders down to - infinity (except the Master) the hiss goes."

That, ^ implies that the Main Out stages of the mixer are not the source of the hiss. The L20 has an output capability of +14.5dBu and whilst that is some 6dB short of most conventional mixers it is surely more than adequate to drive the Adams?
This all points to one or more channels causing the noise so you now have to discover whether you have an intrinsically noisy, i.e. faulty, channel or, whether the source RECORDED on that channel has a poor signal to noise ratio.

Some systematic shunting of channel faders up and down with a 'silent' source should reveal the answer.

Also, beware of phone SPL meters. I calibrated mine by setting it to around 25/30dBC in a room that was subjectively silent to me but then I do have a cheap (Maplin!) SPL C meter to check it with. Two things...you really need the 'C' weighting for music sound testing and 80dBC IS pretty loud in most 'domestic' settings.

Dave.

[Hugh Robjohns]

Clearly, the noise source is the mixer and/or the sources plugged in to the mixer.

First thing to check is the mixer output. Close all the channel faders, but set the main fader to zero. How's the noise now? There will be some, but it should be inaudible at the listening position.

Now work through the input faders one by one. Are any noticeably noisier than the others? If so you may have a particularly noisy mic, or excessive preamp gain.

The preamps are claimed to have an EIN figure of -128dBu, which is pretty good... but then there are lies, damn lies, statistics, and specs...

Naturally, the more channels you have faded up the noisier the mix becomes, partly because of the decorrelated summation of electronic noise, but also the summation of acoustic noise...

...and I suspect that is part of the problem here. We — our ears and brain — are very good at ignoring ambient noise when we're in a room., but mics capture it all and then we're really aware of it when we go i to sound analysis mode!

And finally, 80dBC SPL is pretty blooming loud in a modest domestic room. A figure closer to 70dBC is generally more appropriate and better for your ears. These articles may be of interest.

https://www.soundonsound.com/techniques ... ing-levels

https://www.soundonsound.com/techniques ... w-software

[James Perrett]

Pull the faders down one by one and see which one/ones make the hiss go away.

I wouldn't expect the L20 to be the cause of the problem because it has a fairly respectable Equivalent Input Noise (EIN) of -128dBu A weighted. However, if you are using effects then it is possible that the effects could be causing the noise or amplifying the noise from one of the inputs.

It is possible that the overhead mics, being electret condenser mics, could create some audible noise - If they are the ADX51 then I can't see a noise figure for them in the spec sheet which is a strange omission. If they are the F9 then they have a noise level of 25dB A weighted (presumably SPL) which is fairly high. The Line Audio mics that I use are 9dB quieter than this.

Lastly it could be room noise that you don't notice when you are in the room. We, as humans, are good at tuning out unwanted sounds - especially if they are familiar sounds. Microphones just pick up everything.

Edit - cross posted with Hugh who said pretty much the same thing.

[Wonks]

It may be worth explaining how you have 'gain staged' the input channels on the L20.

There's every chance it's fine, but there may be a better way that produces less hiss.

[CochraneDrumTutor]

These are really excellent replies thank you all, I will run some tests based on the suggestions and report back..

BUT in a quick response to Wonks' question: this was my "Gain staging process"

Each channel is to a different drum kit mic /overhead so I created a raw untreated recording featuring each drum including OHs, then played it back (all within the L20)

I set all the faders to 0 and then track by track noted the overall levels, then tweaked the gain knobs accordingly, rinse & repeat until I had something whereby all faders here showing levels of @ -18Db with the fader at 0.

It has worked well in terms of levels heading to Cakewalk DAW I use too so far.

Thoughts??

Thanks again All.

[CochraneDrumTutor]

Hello again.
After some experimentation I have some interesting findings that I'd welcome you further comments on please:

For context:
Snare mic: https://audixusa.com/products/i5/
OHs: https://audixusa.com/products/adx51/
Audix mic "kit": https://audixusa.com/products/dp7/
"Base" sound level in the room using my totally uncalibrated iPhone using Db-A is @ 28Db.

So onto the findings:
When I had all channels muted and Master at 0Db
No audible "hiss"
When set all channels also to 0D and unmuted them one at a time, they all had tiny amounts of hiss with the snare (i5) and OHs (ADX51s) producing a modest amount more hiss, but nothing radical.

When I unmuted all channels the combined increase in Db to the iPhone-meter was @ +1.75 Db. I think its this "combined" value that I notice, because individually even against a quiet room its not very noticeable.

When I had all channels muted and Master at MAX Db
Some audible "hiss"
When set all channels also to 0D and unmuted them one at a time, they all had modest amounts of hiss with the snare (i5) and OHs (ADX51s) producing more hiss, but again nothing radical.

When I unmuted all channels the combined increase in Db to the iPhone-meter was @ +6 Db. and I had a quite noticeable level of hiss.

So if you have any thoughts on whether these are "typical" / "acceptable" levels?
Or if there some other adjustments I should do, please let me know.

Thanks again.

[Wonks]

Please, please use ‘dB’, not ‘Db’ for decibels.

And if ‘dB A’ indicates A weighting, then you need to realise that A weighting filters out almost all bass and most of the upper high frequencies. C weighting is better and filters out less frequencies, but ideally for noise level readings, Z weighting (no filtering) is best.

[Wonks]

And whilst knowing that the output fader was at its unity gain setting, knowing what the level of gain on the input fader on each channel was, is rather more important.

[CochraneDrumTutor]

And whilst knowing that the output fader was at its unity gain setting, knowing what the level of gain on the input fader on each channel was, is rather more important.

Hi Wonks, so if I'm understanding you correctly you are asking what the fader reading was on the channels during my little experiment?? They were all set to 0 (I just unmuted them as required to trigger the hiss) Make sense?!?! Or am I misunderstanding you?


Secondly, my apologies! dB it is!!! (Wow, I even feel more professional just spelling it correctly! )

Here is some updated readings dB-Z
Base room reading @ 34.8 dB
Master set to 0 with all faders set to 0: +0.7 dB
Master set to Max (+10 dB) with all faders with all faders set to 0: +2.5 dB

(Level on the Master fader I (middle aged drummer) cannot detect any hiss / noise is @ -15 dB)

Thoughts??
thanks.

[Wonks]

And whilst knowing that the output fader was at its unity gain setting, knowing what the level of gain on the input fader on each channel was, is rather more important.

Hi Wonks, so if I'm understanding you correctly you are asking what the fader reading was on the channels during my little experiment??

No, the gain setting on the channels when recording.

The gain knob is the top knob on the line of channel knobs. The channel fader has nothing to do with the individual track recorded signal level (apart from affecting the level on the main stereo mix recording).

It's not the easiest thing to follow but the signal flow block diagram on the last page of the manual shows you where the USB recording take-off occurs.

https://zoomcorp.com/media/documents/E_ ... Manual.pdf

You'll see it's slightly different for SD card recording rather than direct to PC.

Once the data is recorded, the gain knob doesn't affect the recorded channel playback levels (at least according to the block diagram).

I presume you had to both play and adjust the levels, which is why you recorded the performance and then adjusted the gain level to try and get the same recorded level on each track.

It's the gain knob setting that's most important here, not the channel fader level (which were all set to unity), as the more gain you use, the more likely noise will start to creep in (though any noise is unlikely to occur until you get into the upper reaches of the 60dB of available gain.

Can you confirm you are recording at 24-bit word depth and not 16-bit?

And have you got the comp knob turned right down? The compressor can be useful at times when used as a live mixer, but is best left off when recording as software compressors on the track will work so much better and are far more controllable.

[CochraneDrumTutor]

Hi Wonk
OK, here goes..
I'm recording in 24 bit.
Comp knobs on each track are off, yes.

I'd previously set out the channel Gain info in a table and I've put a copy of it here for reference.

https://drive.google.com/file/d/1KCfjWz ... sp=sharing

You will see I used the "Pad" function a lot because otherwise the initial signals from the kit (combined with channel faders to 0) were hugely in the red.

Perhaps these "reductions" in signal strength on the way in are causing an issue later??

Thoughts? and thanks again.

[Wonks]

No, the pad shouldn't introduce any significant noise, it's just a resistor pad and whilst resistors will create noise, it's right down at noise floor level, and the strong signal will swamp that level of noise.

The ASX51 overhead mics are pencil capacitor/condenser mics and these can have a reasonable high level of self-noise. The Audix specs for them don't give any self-noise figures, so it may be on the higher side.

https://audixusa.com/wp-content/uploads ... cSheet.pdf

As these have a -10dB pad on them, and you need to bring the signal level down, I'd use the pad on the mic first and then the pad on the L20 after that if you still need to bring the level down. The mic pad will help stop the signal overloading the mic electronics (and so getting some distortion), whereas the Zoom pad stops the input signal overloading the Zoom preamp.

The max. SPL level of >132dB will be with the pad engages, so >122dB without the pad. Whilst this is very loud, it can be achieved on the peak of the initial transients from cymbal and snare hits, so using the mic pad should give a slightly clearer sound in this application.

Stepping back a bit, you said you get hiss when all the channel faders are at 0/unity when playing back. It's hard for us to know exactly how you've got everything set up in that situation.

Are all the channels set to play back from the recording (and presumably the recording is paused at that point), or are some of the non-drum channels in 'rec' mode, allowing noise from the preamps to pass through? If you have an unconnected mic preamp, that can pick up a fair amount of noise, especially if the gain for that channel isn't turned right down (and you'd typically have it muted or its fader pulled right down).

What's the hiss level like if you have the non-drum recording channels muted? There's generally more work to do on the channels to control noise with a mixer interface than with a straight audio interface.

[CochraneDrumTutor]

Hi Wonks
So I set the switches on the OHs to -10 dB as suggested, and then moved the gain knobs for these channels "2 notches" to @ 1pm which I think is @ +9 dB, getting them back to roughly their prior gain level. (I'd say the hiss these 2 channels now generate is approx. what it was before too)

In response to your questions, I am getting the hiss when faders are set to 0 (unity) under the following circumstances: (See pic)

https://drive.google.com/file/d/1X3Wmcn ... sp=sharing

When the mixer is NOT doing a playback (i.e. there should just be silence).

ONLY the channels (8 to 16) that are active (17 to 20 are not mics but direct channels from an electronic kit and tablet and are not creating ANY hiss at all).

Master is set to 0 too.


So I'm pretty sure the hiss is related just to the "kit mics" only.

So, do you think the levels of hiss I identified in the previous posts is typical / acceptable? OR with the settings I am showing would you want to have zero hiss as you sit at your desk?

If there's any more info you feel is helpful to know just ask. I'm learning a lot here and do appreciate your time and patience.

[Hugh Robjohns]

It's so hard to diagnose things like this remotely.

If you find the hiss objectionable then it's unacceptable.

The fact that you have relatively low channel gains suggests the noise isn't due to the preamps but is either due to some of the mics' high self-noise, or it's natural ambient acoustic noise within the room.

The overheads are the most likely source in both cases... any chance of swapping those mics out for something else?

[Wonks]

My high frequency hearing is so bad that I probably couldn't hear any hiss anyway!

There's a difference between having some hiss on your monitors and having the hiss on your recordings.

If you look at the individual recordings in Cakewalk, where does the noise floor seem to be (with no drums being hit) as opposed to the level when the drums are present? is it really high, or a long way below the peaks? You will definitely be picking up some room noise, which is almost certainly going to be higher in level that any electronics noise from within the Zoom, and there will also be spill between the mics.

You won't want all the tracks playing back at the same level in the mix, (it's rather an artificial situation), so assuming the overheads and kick are your primary sources, I'd pull down all but the kick and overhead, that adjust the kick level to suit the overhead level.

You may want to mix the snare top and bottom mics to a group track so the combined sound can be controlled with a single fader, then add in the other mics to suit (only add what you need to, and don't add anything if it doesn't need it).

You can add expanders or noise gates on the tom mics so you only hear them when they're hit, and that should also cut down the background noise levels when nothing's happening.

One of the first things I do on a recording is manually edit the tracks to ensure any long gaps at the start, end and between playing sections are silenced, with fade-ins and outs between the silence and music so there's no sharp cut-off.

High-pass filtering (and low pass filtering the highest frequencies on things like the toms) can also help clean up the overall sound. Set the high pass filter frequency according to the instrument. I tend to raise it until you can just hear it affecting the instrument's sound, and then back it off slightly.

Hopefully more realistic fader settings will get you to an acceptable (or rather an unnoticeable) level of hiss.

And if you haven't done so, you may want to adjust your monitors' sensitivity so you get an average of around 75dB SPL rather than 83dB SPL, which may help with hiss levels.

Hugh's speaker reference level calibration article (if you haven't seen it).

https://www.soundonsound.com/techniques ... ing-levels

[CochraneDrumTutor]

Many thanks again for all the sage advice on this.
I've taken on-board all the excellent advice and after revisiting some of the channel gains and tweaked the output levels on the speakers I think I've got things to a "sweet spot" where I don't hiss with the Master output at 0, but I do get speaker sound bouncing around the 70-80 dB. range, which does the job nicely.