weird modulation(?) on audio recording - help!

Audacity 2.3.3
OS X El Capitan 10.11.6
Rode NT1-A
Scarlett Solo

Hello, everybody.

Long time lurker, first time poster. I’m sorry if this is in the wrong bit. If it is, I hope someone will move it to where it’s supposed to go.

I’ve just started audiobook recording. I’ve got myself a book to record and and I’m having so much trouble. I’m using a brand new (as in arrived today) Scarlett Solo/Rode NT1-A set up into my MacBook Air and I’m seeing and hearing a weird crackle on some of the recorded audio. The thing is I’ve heard this on another setup (my first one that turned up last week) with a Rode NT1 and AI-1 that made me call Rode and see about sending the Ai-1 back as I thought it was up the spout.

I’m at my wit’s end as I thought if I replaced the mic and interface that would solve the problem, but lo and behold it’s on the recording I’ve just made too. That means I think there’s something I’m just not doing and I can’t for the life of me figure out what it is, as two brand-new mics and interfaces can’t be up the spout. And I can’t afford both, so I’ve got to return or sell one on.

I know my way around Audacity in the most basic fashion as I’ve used it for little audio edits and fiddling over the years but this is the first time I"ve used it in anger and I’m having so much trouble with this.

Can anyone please tell me what the matter is or what I need to configure?

Today as prep for this recording session, I did a full reinstall of Audacity 2.3.3 and optimised the Mac - hard disk first aid, removeded all junk files. Got it all clean and tidy. But then this.

I’ve attached a screenshot of the weird waveform, it looks all torn up, and a .wav of the troublesome audio for investigation. Specifically the word ‘follow’, that’s where I heard it and nearly burst into tears today. Which is a surprise as I’m in my 40’s.

So I signed up here instead.

edits: context/typo

Screen Shot 2020-05-16 at 22.39.53.png

If you mean the constant ~20Hz ripple, than can be removed with a rumble filter in Audacity …

high-pass aka ''rumble'' filter.gif
<20Hz is not audible, but you should remove it as it can interfere with processing.

Hello, Trebor!

Thank you! I had a think last night after I posted and I noticed that both the AI1 and the Solo were outputting at the maximum sample rates so I changed them to match the project file (44.1) and changed bit depth on the project to 24-bit and I thought that I’d sussed it, I did sound much better.
Screen Shot 2020-05-17 at 00.09.04.png
Screen Shot 2020-05-17 at 00.04.25.png
But after starting recording again today, I’m SURE I’m still hearing something.

So a 100hz rumble filter will clear that tearing up? I tried it on a clip and I’m not sure I can hear a difference, but maybe I’ve gone earblind - I’ve heard myself so much lately! And I’ll be hearing more as the deadline is Wednesday for this!

Do these units put out this 20hz rumble you’re talking about, or is it something from my recording space? Its a cupboard 4ft x 4ft x10ft (tall) that I’ve deadened as much as I can with with acoustic foam and blankets and earlier records have been alright, it’s just since using BOTH these interfces. That makes me think that it’s a problem with me and my set up.

…and to follow on, I did just run a 100hz rumble over my posted clip (weird follow) and I didn’t hear any difference to it. Mind you, comparatively today’s records DO sound much better, so maybe just giving Audacity the right incoming audio has helped…? I’m still not sure, but I’m second-guessing myself constantly at the moment.

…as this is about audiobook production, should I also post there?

We prefer to avoid duplicating topics. The regular contributors to the forum will see your posts whichever forum board you use, so there is no benefit to duplicate posts.

Do you still require help with something?

I’m sorry, Steve. I’m having a right old flap. Yes. I do.

I’ve just done another recording using the Scarlett and althought that sounded good, the file I’m editing now doesn’t, I’m sure I’m still hearing this tearing. It MUST be something to do with the way I have the interfaces set up, I thought that making the appropriate changes in the Mac MIDI settings - as I’m sure I saw in the Scarlett paperwork, but now can’t see at all - would do the trick, and as I did this to both the AI1 and the Scarlett last night and they sounded fine I’m now tearing my hair out when I hear it on other recordings.

Can you see anything wrong in the screenshots I posted regards the input settings? Am I even on the right track making sure the audio coming out of the interface matches the settings for the project? I mean it seems to be common sense but I have very little experience with Audacity’s deeper features aside of importing a .wav or .mp3 for tweaking; actually recording using Audacity seems to have me stumped. The funny thing is before the audio interfaces arrived I was using an H5 as a (somewhat noisy) interface with no trouble so I can’t see what can be wrong. These should just work to feed audio into Audacity, surely? I mean they say plug and play…

Sorry if I seem a bit like I’m raving, this has had me on it’s horns since Wednesday

Normally Audacity should be set up to record as 32-bit float. See: Quality Preferences - Audacity Manual

Please post a short sample in WAV format so that we can see / hear what you are referring to.

Steve, thank you.

I will post a .wav when I can isolate a good example of what I think I’m hearing now. There was a sample posted initially in the post at the top of the page here, you can hear it most on the word ‘follow’, now I think i can still hear a smiliar thing on the records I’ve today but I think I’m starting to go barmy and need to edit something rather than just endlessly rerecording and getting upset.

So let me ask some questions that might help me understand more. I thought that if the interface is set to 44.1/24-bit and the project is 44.1/24, they’d be compatibale, like setting your video edit timeline to match the format of the video you’re editing (I’ve always been more video than audio). And that was the explanation I gave myself when files sounded good last night, is that not the case with audio? Is 32-bit better? Do the project settings matter with an Audacity project? That sounds daft, but I mean if a device is putting out 96kHz/24 - like the AI1 was intially - will that make any difference if fed to a 44.1 project?

The ‘follow’ example above was from project settings of 44.1/32 with the Scarlett putting out highest sample rate, would that cause that distortion on the clip I posted at the top of the thread? If not, what? Has to be something I’m not doing right and that’s what’s messing with me the most.

here’s one that just popped up, the world ‘ultimately’.

I mean what on earth?!

And I like dogs, but I’ve been doing this training book for ages and I’m going off them fast.

FWIW, deleted the double post in the Audiobook forum. New here and don’t want to be a pain.

okay, so do I set the interface to 44.1/24 and have my project set at 44.1/32?

What is the difference?

Yes, that’s fine.

The main benefit of working in 32-bit float is that it can handle signals over 0 dB, so, for example, if you apply an effect or mix some tracks and the result goes over 0 dB, then you can simply Normalize, or amplify by a negative amount to bring the audio back into range. On the other hand, with 24-bit (or any other integer format), if the process or mix went over 0 dB, then the audio would be permanently damaged because integer formats can’t go over 0 dB - they simply clip off peaks at 0 dB.

The recording level is a little low, and it could benefit from a sub-bass roll-off filter, but other than that it seems OK to me.
We normally recommend the “Low roll-off for speech” preset in the “Filter Curve” effect, though you may of course create your own curve if you prefer.

How are you listening to your recording? Headphones? Speakers? Make / model?

Thank you for explaining the bit depth thing. I thought the interfaces would be putting out too much signal, if you like, if set to higher output rates, like putting a teaspoon in a firehose stream and that was what was causing the distortion; too many bits for the project bitrate. But if that’s not the case, I think I’m overthinking it…

…so did you hear anything ON the word "ultimately’? Because I sure do when I’m on cans, as did someone I asked to listen. Does anyone else?

I use my old monitoring headphones, a pair of Sennheisers, the HD25-1. Part of my old broadcast kit, always use them for editing. See that’s the thing, I’ve worked in broadcast for years, shot and edited my own stuff and now dealing with hard-core audio editing (well, it’s not even that, currently it seems to be that I’m incapable of plugging a device in and having it work properly)

I apply the low roll-off as part of the ACX mastering procedure. But even after that it’s still audible. I’ve checked with the Sennies, a pair of gaming heaphones and even some iphone headphones and there’s something there… And to be honest, I wouldn’t know what a different filter curve would do!

The record level IS low, but I find that applying the ACX workflow (I assume the RMS normailsation) bumps that up to peaks of about -6 to -3. And I’m conscious to keep the noise floor below -60; I use the RMS settings for the record monitor level as I’ve seen elsewhere here to do, I think it’s low-level myself as well - but anything higher sounds blown out after applying my macro.

See the thing is, I’ve been using a Zoom H5 as my interface or recording straight to SD card with a camera mic (NTG1 shotgun, bit noisy so wanted better stuff) and editing that way, I wanted to take a more pro approach and get the right kit; so decent(er) mic, (NT1 and AI1 kit, then the panic buy of the Solo and NT1A) but running BOTH systems into the computer and I get the same distorts and jaggy-sounding recordings, apart from one record last night when I modified the output settings of the interface, as written a few posts above when I thought I’d cracked it, then that distortion on the word ‘ultimately’ in the clip posted during an edit today…

I just can’t understand the issue. I don’t even think it’s the laptop as, as said, I’ve used the H5 as an interface with no troubles. Plug and play seems to be not the case.

edit: typo

Now I get it: When the volume of your voice goes above a threshold there is a some harsh resonance.

Possible causes of resonance …
Headphone leakage, (as an experiment try speaking at different volumes in the booth without headphones).
Reflected sound within the booth, (try moving the mic closer to the centre of the booth, or thicker insulation).

The booth is a coat cupbboard I have treated with acoustic foam and blankets, not ideal but much more snug than before and quiet enough. The thing I don’t get it that this resonance happens on with different mics and interfaces and mic positions…

And recording witht eh H% doesn’t seem to produce the same essfect. That makes me thingk there’s trouble with the computer, as I say two seperate interfces can’t be duff.

Any Mac users out there who can tell me if it’s a good idea to trash my sound preferences, maybe? I’m not going to do anytihing like that 'til this record’s donr though.

The resonance effect will be dependent on …

The frequency-response & sensitivity of the microphone.
The position of the mic in the booth.
How big the booth is.
How reflective the walls of the booth are.
How high you have the gain on the interface, (i.e. we’re back to mic-sensitivity).
How loud you are speaking.

Unless the source is sound leaking from your headphones, the cure is an acoustically-dead booth.

Well, I was just doing another record and I noticed this resonance pop up again…

I won’t post it here because it’s the same as in earlier samples. It has to be the mic position I guess, as I wasn’t using a new (Rode/Scarlett) interface, the idea was to keep things as they were and just change the mic. I’m using TWO Rode mics, NT1 and NT1a and getting the same thing. I’m unsure as to how frequency response and sensitivity will affect resonance; I’m just used to plugging them in and filming or talking.

Current setup that I heard this resonance on was the NT1 with a Zoom H5 acting as an audio interface. Record level on the H5 was set to 5, as I’ve said in other posts, that’s about the best the H5 offers as a preamp without being too noisy in my earlier set up. I was using an NTG1 and noticed lots of hiss in earlier experiments that I thought would be distracting to a finished audiobook, so ‘get better mic and interface’ was the thought that caused all this in the first place.


Mic was in its usual position; facing a rack of (covered) coats with a wall of acoustic foam behind me and the mic. A upwards-mounted Rode boom pole (i.e., base of pole is a few feet above my head) holds the microphone and the boom pole is held in place by tension against the foam on that part of the wall and the rail the coats are hung onto. I’m presenting to the mic centrally, and the mic is held in a SM1 mount.

I do have a boom arm that I’m intending to use, but I have yet to figure out how to mount it in there; the boom pole and shock mount seemed an acceptable compromise.

I’m approximately 5-6 inches away from mic (three inches from popshield) and headphone monitoring isn’t too loud (I don’t think). I’m not shouting, indeed this current recording sounded a bit flat and depressed(!), but I’m projecting a touch as I read, as one would. Peaking about -12 to -10 on the Zoom. When setting record levels direct to Audacity, I’ve been using a guide I saw here somewhere about setting the record monitoring to RMS and keeping the red line under -60 (including the darker bouncing bit), so that’s where I’ve been settimg record level on the interfaces.

This current record was to SD card and import into Audacity, so it HAS to be how I’m dealing with the mic, I guess.

The dimensions of the room are 4ft x 3ft x 8ft (it’s tall but there’s foam all the way up and over the ceiling. There’s occasional bumps or clatters from the next door flat, but nothing at all that would distract, occasional noise from a water pipe. But I notice and stop when that happens)

But the thing is I"ve noticed this ONLY on the NT1 and NT1A, never using the NTG1.

Should I face it the other way, towards the foam?

Sorry for the wall of text, but when I’m troubleshooting, more info is better than less. But still, sorry.

edit: dimensions

If you try a short experimental recording with headphones unplugged you will be able to tell if headphone-bleed is the source of the problem. During the experiment include recordings where you raise your voice, (the objective is to see if the resonance effect can be deliberately caused).

You haven’t specified the thickness if the acoustic foam. The 1" stuff is helpful, but it’s not professional standard.

Mike “booth-junkie” DelGaudio was using solid 4" stuff …