Will this pass ACX scrutiny?

Hi everybody, I’ve just set up a studio to narrate my own book, and I’d looooove to know if I’m meeting ACX standards. Attached is a 10 sec sample (2 secs room tone), both raw and processed.

  • AT2020
    Zoom H4N used as preamp
    Windows XP
    Audacity 2.1.0

I followed the advice here https://forum.audacityteam.org/t/meeting-acx-requirements/38239/8 for the processing:

  • Effect → Normalize -3.2
    EQ: LF rolloff for speech
    Noise reduction: 12, 6, 6
    NO COMPRESSION as it raised the RMS above -18
    Effect → Normalize -3.2

It sounds good to me, but what do I know? I’d really appreciate any feedback.

Sometimes it’s best to submit first. If I do it, I’m almost always going to suggest milder corrections than you.

The “raw” submission is really, raw, right? Press Stop after you get to the end and File > Export? We had one poster who admitted, after intense grilling, that he “adjusted” the clip with the volume sliders “to make it easier for us.”

He didn’t make it easy.


Yes, I think you’re working too hard. Attached, corrected, which passes all three checks.

Effect > Normalize > [X]Normalize to -3.2 [X]Remove DC
Steve’s Rumble Filter
Noise Reduction. 6,6,6. The Noise Reduction Of The Beast.

If you could get rid of that hum, you wouldn’t need the Noise Reduction at all.
Attach 2 is where I left the hum in. It actually passes ACX Noise (not by much).

Effect > Normalize
Steve’s Rumble Filter.

That’s it. We’re done.

Play the second clip and turn the volume up during the silent lead-in. Now do that on the first clip where I took the hum out. The main difference is that low level mmmmmmmmmmm.

So which fans, lights, or refrigerators can you turn off? Is your computer fan running?

I’ll get to the rumble filter.


You understand that we’re going to want you to tell us how you did it? This is right up there with the clip that I made, oddly with the same hum problem.


I more or less located the source of my hum by running the system in monitor (where it doesn’t actually make a recording) and then wave the microphone around with my headphones cranked to max.


Right-click the top meters > Start Monitor.

For one example, if you lift the microphone from the desk and the hum instantly vanishes, then you need vibration isolation of some sort. The desk is moving. You may be able to get a formal one for your microphone, or several layers of bath towel under the microphone can be effective. Remember, you pass noise just as it is, just not easily and I can still hear the hum.

Oh, you already have the LF_rolloff…


Are you using the H4n to record, or passing on the sound to Windows? There are many, many sound problems caused by the computer and if you can avoid using it for recording at all, it’s probably a good thing. I use the USB connection strictly for transporting already existing sound files.

Did you do anything special to the room?

So this should be a piece of cake. Plug the headphones into the H4n and walk around. Or, if you’re insanely lucky, the hum will go away when you turn the computer off.

I should warn you not to connect an XP machine to the internet.


Firstly, thanks for your feedback. I take it you found no problem with room echo or coloration.
“we’re going to want you to tell us how you did it?” How I did what???
There are two possible hum sources: fridge and laptop. Attached: 3 samples with fridge, laptop and neither operating. Using Plot Spectrum, I get -66.8, -71, -72.1 respectively. I’m downtown, so traffic. I’ll try a late-night test for comparison.
A pic of how the laptop is isolated:

Just found your last two replies. Those are interesting suggestions. The AT2020 is in an AT shock mount on a Neewer anglepoise-like stand, seems well isolated to me.
I’m using the H4N just as a preamp, but I’ll try recording to it and see. Have to leave for a meeting, so tomorrow. (As an aside, I was getting a glitch every 1.4 seconds on it; turned out my SD card was too slow.)
I know XP security is poor. I’m not using a browser at all; the laptop is just a digital recorder, and I do all my work & browsing on a Win 8.1 desktop.
Yes, the room is treated, see pic. Studios don’t come smaller than this!

I applied.

Effect > Normalize > [X]Normalize to -3.2 [X]Remove DC

to ‘Neither One’ to force the blue wave peaks to conform and the other two numbers fell in.

So that’s it. With just the slightest volume adjustment, you created an ACX conforming test clip.

The background sound (room tone) is a gentle rain-in-the-trees rush sound. Easily ignorable.

I did not test to find which one is creating the hum. I’ll do that now.

I have a new analysis tool I’m trying. Attach 1 is the peak and RMS (loudness). Attach 2 is the noise.

-3.2dB, -18.69dB, -62.2dB

All three pass.

Screen Shot 2015-05-07 at 19.23.13.png
Screen Shot 2015-05-07 at 19.21.47.png

I’m on my fourth pass…

None has -66.3dB noise.
Fridge has -61.2dB noise
Laptop has -66.3dB noise.

So the pint chiller appears to be making the low level hum. You can do this yourself. Drag-select from half-second to 2 seconds.

Analyze > Contrast > Measure. Read the value > OK.

I’m starting to lose it. Time to watch some British TV and have a pint of my own. I should have the new Murder in Paradise by now.


You are confirmation that the H4n has superior microphone (fffff) noise compared to my H4. I would not be preparing a show with an XLR microphone plugged into my H4. I tried it and it was too noisy.

In case I didn’t say so earlier, with the banishment of the fridge, you could be one of those mythical people that can apply the rumble filter, adjust the sound levels and out the door.

You could still fail ACX by messing up the timing, file name protocol, Room Tone segments, etc, but I think the sound is fine.

Your story-telling seems to be spot on, so…



Effect > Equalization: LF_rolloff_for_speech, Length 8191 > OK
Effect > Normalize: [X]Remove DC [X]Normalize to -3.2 > OK

File > Export.

We do warn people that even though an ACX submission is MP3, your own home archive should always be WAV. WAV can be made into anything else. Re-editing an MP3 causes problems.


That is so cool, thanks for all your help! I started on my ACX samples today.

Do post back the results, good or bad. If bad, tell us the exact complaint. Your tracks have enough leeway to do simple changes without upsetting the voice or performance.


Hi, just found your latest posts. One of those mythical people, huh? Wow. I attribute it to several things.

One, I ran a demo studio 45 years ago(!) using two 15ips 2-track machines, so I understand acoustics. I still have an AKG D12 as a souvenir. Secondly, I volunteered weekly for several years at Recording For the Blind & Dyslexic, which helped with reading skills.

Against that, I have moderate hearing loss. Rolls off at 2K, 7K is the absolute top. Hearing aids help a lot, but they introduce distortion and still don’t take me past 7K.

Sure, I’d be happy to let you know the results. I haven’t submitted yet, it’s been a crazy weekend.

You’re not the only hearing-challenged performer.

“Sure, your voice sounds fine, but do you hear that buzz in the background?”

There are ways to work around this, but they take a bit more talent/experience. 120Hz power hum has a distinctive pattern in Analyze > Plot Spectrum (attached). Click on the graphic. Note the lump at 60 and a much larger one at 120. There’s also a smaller one at 240, etc. But 120 is the taller one.

That specific one is generated by the Giant Hum Monster that Lives in my Attic. That’s how it seems. It’s probably really the high tension wires over the house.

Any purple activity below 20 Hz is trash. Steve’s rumble filter (LF_rolloff…) kills off everything below about 100Hz which is pretty common. Nobody in Hollywood would dream of shooting anything without the rumble filter. It varies between 80, 100, and 110, but there’s always one.

And etc. Newbies are always holding their speakers and headphones with a death grip. I don’t recommend this, but I have made a professional recording without hearing a thing. I know exactly where my meters and instruments are supposed to be and how they’re supposed to act.

Ideally, I’m watching and listening.

Screen Shot 2015-05-10 at 18.42.31.png

Also regard the hum problem you had. You made several different clips with equipment turned on and off and all I did was make the software tell me which had the higher loudness. I could have done that without even knowing it was hum.


Took a while to get my act together, but I sent in a 5-minute sample, and it passed! ACX replied:

This is great overall, I only have two notes for you. First, keep in mind that we require half a second of clean room tone at the top of each file, and 1 to 5 seconds of clean room tone at the tail of each file. I also feel that the chapter heading sounds like it has been faded in, or that you may have been off axis for a moment. I’d recommend another take for a stronger impression.

Other than this, you seem good to go! Thank you for taking the time to submit your file for review.

Thanks so much for your advice and reassurance! Phil

First, keep in mind that we require half a second of clean room tone at the top of each file, and 1 to 5 seconds of clean room tone at the tail of each file.

See? I told you if you were going to mess this up it would be your own fault.