Understanding Waveform and Loudness

Sorry for all of the questions, but ever since I got two newer Retina Macbook Pros I have had nothing but issues with Audacity and recording Internet radio streams (and phone calls) and I really could use some help getting things working once and for all.

As part of that, I guess I need to better understand sound stuff and how Audacity actually works. (In the past, Audacity was simply “plug-and-play” on my oldest MacBook pro, but not so much so on my newer MBPs…)

So tonight I am recording an Internet radio to see how things working on Retina MBP #2 and I noticed something interesting…

When I record the stream, the amplitude (?) of the blue waveform is only at 0.5 (whatever units) yet the “vloume meter” (??) is peaking in the yellow and sometimes red.

See attached.

First off, as I learn more about audio, I hear everyone talk about things like “-6dB” and yet I don’t know what units or the significance of the whol -1.0 to +1.0 scale is when I record.

Can someone explain that to me?

And back to my OP, why is the waveform not very high yet Audacity makes it look like it is clipping?

And when I play things back, the recording sounds much louder than the blue waveform indicates.

Again, on my ancient MacBook Pro I don’t have any of these issues, but my OS is so old that my old Mac no longer works with websites and stuff, so I gotta get my newer MacBook Pros working so I can decomission my old MBP.
Low Amplitude yet -3 dB (2).jpg

First off, as I learn more about audio, I hear everyone talk about things like “-6dB” and yet I don’t know what units or the significance of the whol -1.0 to +1.0 scale is when I record.

The blue waves are in percent and there is a relationship between dB and percent. Three important ones: 100% is 0dB and dB (that we use) gets quieter in negative numbers.

50% is -6dB, and the blue waves run out of poop (technical term) at about -25dB. That’s right. The blue waves won’t measure anything quieter than about -25dB. That’s where the graphics turn into a flat blue mush. Quick look at the bouncing sound meters will tell you that sound keeps getting quieter down to -60dB or so and it actually goes way more quiet than that. You can set Audacity to show you the whole thing if you want.

The blue waves actually work out pretty well because most of the important sounds happen in the loudest 25dB.

This is a thing I wrote about the audiobook sound values. This is a real-world measuring system based on a commercial product.

I don’t know how you can have a mismatch between the sound meters and the blue waveforms. I can make up something. If you zoom into the blue waves far enough, you may find a tiny sharp loud sounds that the graphics can’t deal with but the meter is fast enough to pick up.

I’ve never seem them not match. You’re a celebrity unicorn.


Try this.

Genrate > Tone: 400Hz, Amplitude 0.5. any short time > Enter.

That should give you a 50% tall wave and if you play it, a -6dB sound meter.

Does it?

Koz

I glanced over this. The blue waves represent the vibrations of air at, for example, your mouth. Higher and lower air pressure as you speak or sing. If you plug a graphing meter into a microphone and sing into it, it would show you the blue waves.

It gets magic because some people speak with uneven up and down waves.

This is the latest example of good voice recording practices.

This illustration was taken from an actual voice performance. Please note the up and down parts of the waves aren’t even. There are more ups than downs. That’s normal for this performer.

Koz

Trying not to keep going different rabbit holes…

Why is 0 dB 100%?

To the layperson, 0 dB would be complete silence, no?

I thought a jet was like +70 dB?


So at what level should my edited waveforms be?

Historically, I usually shoot for peaks - minus occassional blips - at maybe 80-85%. (It’s hard to explain, but I just use my eyes - and gut - and amp things up so they are a tad under 1.0.

Hope that is “correct” because that is what I have been doing for the last 13+ years… :open_mouth:


Actually I just changed Audacity to: Preferences > Interface > Meter dB range = -36 dB so it is easier to read on my old eyes.


Yeah, I never even really noticed the “sound meter” - is that what it is called - at the top. I just go off the blue wave forms when I record and when I edit.


I feel like my 1-2 threads are growing onto lots of trheads.

My (ideal) end goal is by coming Sunday is to have Audacity completely working on both Retina MacBook Pros so that I can record Internet radio shows and not get missing files like in my other trhead AND to have it so I can record phone calls.

On my 2nd Retina MBP, I will leave it recroding over night and see what happens to the recording. (It has Loopback v2.0).

My 1st Retina MBP is the one that is totally screwed up on recording Internet radio shows and phone calls, so I guess it amkes sense to get my 2nd Retina working first then copy those settings.

In addition to my multiple trheads on here, where should I strat in my reading to help me solve these issues? (I don’t want to go too far down paths that won’t help me get things working, as that is my 1st goal. I can learn more about sound engineering over time.)


Welcome to my complicated life… :frowning:


Am recording a radio show tonight, but will report on that homework assignment in the morning.

Why is 0 dB 100%?

I think that’s convention. 100% is pretty obvious, as loud as you can go, etc, 0dB is where the digital system runs out of numbers on the way up. It’s digital clipping or overload. The digital system stops following the show.

I thought a jet was like +70 dB?

See my weaselly words: “The dB that we use.” That other one is dBSPL. Sound Pressure Level. Sound in free air. That one starts at 0dB so quiet that nobody can hear it and works up. Threshold of pain, etc. etc. There’s special meters to measure that and that’s the one burned into Health and Safety laws.

There is no relationship between “our” dB and dBSPL.

amp things up so they are a tad under 1.0.

Works for me. Overload (clipping) sounds awful instantly, so if you like the way the shows sound and you don’t have to meet anybody elses specifications, you win.

-36 dB so it is easier to read on my old eyes.

Again, if that works and you don’t have to meet anybody elses standards, you win.

I feel like my 1-2 threads are growing onto lots of trheads.

Describe brain surgery. Be brief. The difference between a casual user and sound technician is what happens when things don’t go well. Only one is likely to walk away with a show.

Internet radio shows and phone calls

Macs don’t have any natural, built-in way to record streaming audio (Youtube). You always have to add sound routing software or take extraordinary measures—or do it in hardware. I don’t think I have a picture of a loop-back cable. That’s on my 2-Do list.

https://manual.audacityteam.org/man/tutorial_recording_computer_playback_on_mac.html

Nobody can record phone calls. The most reliable way to do that is over a service such as Skype or Zoom and then get Skype or Zoom to record them for you. Zoom will actually record each side as a separate sound file so you can mix them into a finished show later. Production hint. Always wear headphones on a call. It makes your voice sound better to the far end (even if you can’t tell) and it makes a better recording because Zoom doesn’t have to do any feedback suppression. Do it in a quiet, echo-free room and it doesn’t have to do as much noise reduction and echo cancellation.

You can do it in hardware which is how most broadcasters do it.


Yes, it’s crazy, but it has three advantages. It doesn’t matter which voice service you use (this one was Skype), it’s dead reliable (push this button, record this call, go to lunch), and has very high quality. Denise and I are on opposite US coasts (this was an engineering test).


Koz

Yes, I tried this and the tone at 50% is also at -6dB.

But as you can see in this latest attachment, the blue wave form on my 2nd Retina MBP doesn’t seem to match with the sound meter…


In this screenshot, I would say the blue wave is at about 25% yet the sound meter is showing -6dB.

When I listen to this recording from last night with my headphones set at volume = 50% on my MacBook, the volume is a little on the loud side.

That doesn’t seem right, and if I think back to over a decade of recording radio shows on my old MacBook Pro, when I produced the final radio show, I usually amped up the blue wave form to say 85% and the loudness of those files sounded similar to this latest recording on my 2nd rMBP at these lower levels…

Koz,

Thanks for the picture and thoughts on phone calls. I shouldn’t have brought up recording phone calls since my threads keep exploding into other ones?!

I would definitely like to come back to thi=e phone thing later in another thread.

For know, suffice it to say, that you CAN record phone calls using Loopback (or formerly SoundFlower) and I have done this for years, although I haven’t quite gotten it to the level that I want it.

(You guys keep saying you can’t record on Macs, but this IS a Mac forum and I HAVE said several times that Loopback (and SoundFlower) allow you to record on Macs, so in a Mac forum I assumed that everone knew that… :wink:

P.S. Nice sounding recorded phone call.

You guys keep saying you can’t record on Macs

I said you can’t record on Macs using internal, native services. I’ve been using Soundflower for years and iShowU. I didn’t know about Loopback.

you CAN record phone calls using Loopback.

Good to know. How? One hitch in Audacity’s gitalong is the need to do it on all three computer platforms. That can be a strain for boutique software producers.

Koz

Not sure what the file upload size limit is on this website?

Am going to try and upload a zipped snippet of me recording KKTX-FM last night. (Included is the .aup file plus a screenshot of what it looks like when I play it.)

Maybe that will help you to see and hear what I am dealing with last night and what this thread is complaining about…

File too large. :frowning:

What is the file limitation size? And can it be increased? I have 4.6MB and 8.6MB files that I wanted to share here…

Mostly 2 MB, though it may be 1 MB in a few cases.

You could use a file sharing site such as dropbox, Google Drive, One Drive, SendSpace or similar, and post a link to the file. If you do that, ensure that downloading is enabled for “anyone with the link” or “public”.

Tip:
When sharing a large file on a forum, be sure to say in the post how big the file is - people with slow or limited Internet can be quite annoyed by unexpectedly large files,

Can you guys up that to say 4-5MB? (Which is pretty tiny in 2020…)


Something I will have to look into, but not an option right now as my brain is overflowing with issues that need to be fixed already!

I exported my .aup as an .mp3. Not sure if that will help you to help me.

Here is a brief recording of KKTX-FM from last night and it matches the screenshots above. (1.3MB)

rMBP2_KKTX_2020-11-22 (sm).zip

It includes the .mp3 plus a screenshot of what things look like in Audacity as I listened to it.
rMBP2_KKTX_2020-11-22 (sm).zip (1.29 MB)

It’s not tiny when you have thousands of files, thousands of visitors, and you pay for the bandwidth. Audacity is not a business - the software, support, documentation and websites are all provided free of charge (many thanks to those that donate and support Audacity).

Nice sounding recorded phone call.

Thanks. Denise and I are ringers. We’re both broadcast professionals. Denise was, I think, Music Director at WWDC when they gave Howard Stern his first real broadcast job. We’re both in reasonably quiet rooms and we’re both wearing headphones. This is not our first rodeo.

That’s how I know this works. The music was a mistake. I wanted to see how much stuff I could cram into a single, real-time recording. The recording computer (on the left) had the playback channel left over, so I jacked it into the mixer and played music—badly as it turned out. I should have put Denise on the left and me on the right and mixed it all down later.

Koz

In this screenshot, I would say the blue wave is at about 25% yet the sound meter is showing -6dB.

I think the meter is showing the peaks and you might not see the waveform peaks unless you zoom-in.

The easiest way to check the peak is to run the Amplify effect. i.e. If Amplify defaults to +6dB, your current peak is -6dB (and you can cancel the effect if you just want to check).

Or, the optional [u]ACX Check[/u] plug-in will give you the peak, the RMS level, and some other information.

When I listen to this recording from last night with my headphones set at volume = 50% on my MacBook, the volume is a little on the loud side.

That doesn’t seem right

Perceived loudness is related to the short-term average (or RMS) and the frequency content. For voice, RMS is a good proxy for loudness but it doesn’t take frequency content into account. (Our rears are most-sensitive to mid-frequencies.) There is a loudness measure called LUFS which does take frequency into account. And, there is a Loudness Normalization effect that allows you to set the LUFS loudness. But as-of now, there is no way to simply measure it without using a 3rd-party plug-in.

Here is another snippet (attached) of a recording that I did a decade ago… (1MB)

MBP_OffTheRecord_2010-07-25 (sm2).zip

Notice how on this one the blue wave form is much closer to 1.0 than on the previous attachment from last night?

Now I must confess that this one sounds a bit distorted, and it looks like there may have been some clipping, but back to my confusion above…

Why does the recording of KKTX-FM have such a low (i.e. 25%) wave form yet sound so loud in my headphones, yet this “Off the Record” recording have a waveform that is at maybe 85% and the loudness is the same?

Also, the screenshots show something flaky between the blue wave forms and the sound meters…
MBP_OffTheRecord_2010-07-25 (sm2).zip (1.01 MB)

this one sounds a bit distorted

That’s because it is distorted. The track has peak clipping or limiting. See at 19.7 seconds, all the wave tips are exactly the same height?

Screen Shot 2020-11-23 at 9.14.57 AM.png
The bouncing sound meter isn’t measuring high volume sounds because there aren’t any high volume sounds. Something in the system squashed them.

I think the meter is showing the peaks and you might not see the waveform peaks unless you zoom-in.

What he said.

Koz

Hey, I recorded that sample 10 years ago and was still new to the concept of “clipping”.

My point is that why is the wave form so much higher in the “Off the Record” sample (i.e. 85%) compared to the sample I recorded last (i.e. 25%) and yet the seem to have the same “loudness” when I listen to them with my headphones?


To further prove this point, here are 4 screenshots showing the sample I recorded last night…

1st screenshot shows the original wave form

2nd screenshot is me choosing “Amplify”

3rd screenshot is me listening to it after it is amped up - notice the yellow and red

4th screenshot is me listening to it after it is amped up - with another screenshot showing it going red


Questions:
1.) Why is the waveform at 25% yet the “loudness” at volume = 50% is a tad loud? (Anything I recorded on my old MBP at 25% waveform would be very hard to hear…)

2.) If I used Amplify, be default it should NOT clip, so whyis the amped version going into orange and red?

3.) Why is the amped up version so incredibly loud when I listen to it? (I had to adjust my volume to 25% so it is pleasant to listen to.)
rMBP2_KKTX_Amplifying.zip (509 KB)

whyis the amped version going into orange and red?

The colors are not a guarantee of sound damage. They’re a warning.

Audacity has a couple of those.

The timeline has View > Show Clipping. If you perform too loud, Audacity will place a red bar in the blue waves at the event.




This tool operates in the subjunctive. Since in the real world, you can’t actually go over “0dB” (no more digital bits, right? They’re all used up). The best Show Clipping can do is guess at it. “This sound would have created clipping damage had it really, truly wanted to.” Back here on earth, that usually means sensing three or more digital values in sequence at exactly 0dB. No sound in nature can do that, so it must be damage.

But wait. There’s more. You can go over 0dB as long as you never leave Audacity. Audacity uses 32-bit floating (don’t worry about it) internally so that effects, filters and corrections don’t create damage accidentally. Say you applied a filter that boosted some musical tones and the waves got too tall when you did that. The next step can be a volume reduction to bring the waves back down and everything is happy. The clipped sound isn’t lost. Audacity is just saving it until you decide what you’re going to do. If you tried that trick outside Audacity, say in your sound mixer, it would destroy the music.

This also means you have to make sure your Audacity show is “legal” before you make sound files. No red bars.

Koz

Koz,

Yes, I am familiar with that option.


That is all good to know, but can someone please answer my questions in my last post at: Mon Nov 23, 2020 12:53 pm

Thanks.