Converting 16-bit to 8-bit issue

GoldWave general discussions and community help
marera
Posts: 8
Joined: Tue Feb 02, 2016 9:47 am

Converting 16-bit to 8-bit issue

Post by marera »

hi everyone,

I need short passages of spoken text in PCM 8 bit unsigned mono at 22050Hz, to be stored in an industrial alarm-device.
The device only handles this format.
No-one and no-thing seems to be willing or able to record in 8-bit, therefore I need to convert.

No problem this far, GW converts sample-rate, mono, 16 bit PCM with no problem.
But I found out that there is one single step in converting blasting the sound: 16-bit to 8-bit.
It gives an unpleasant hiz in the output-file. The hiz is not constant, but the louder the voice, the louder the hiz
Using the hiz-filter has litle effect and makes the speech even more un-understandable.

What can I do to get a better convertion?

I could post files before and after, if I only knew how to attach file in this forum?!

Thanks
Marc
2leftfeet
Posts: 149
Joined: Sun Jan 20, 2013 10:28 pm
Location: Napier New Zealand

Re: Converting 16-bit to 8-bit issue

Post by 2leftfeet »

Hello Marc. I think that you might be making the original recording level too high. I had to do the same thing some years ago and this is what I did:-
1] Record your message at 22050Hz making sure that you do not record at high level (VU meter about 40%) and make sure that it is good quality & noise free. Now adjust the audio level to 90%. using the "Maximise volume" button.
2] Select “File save as”.
3] Left click “Attributes”.
4] Choose PCM unsigned 8 bit mono option from the drop down menu and save the audio clip. If the original audio file is good quality and noise free, you should have a good result for your alarm.
DougDbug
Posts: 2172
Joined: Wed Feb 16, 2005 3:33 pm
Location: Silicon Valley

Re: Converting 16-bit to 8-bit issue

Post by DougDbug »

Check your recoding levels... If you run Maximize Volume after recording and the current maximum is 0dB, you are probably clipping (distorting). If your recording is clipped, the best solution is to start-over and record again at a quieter level.

Typically, your peaks should hit -6dB to -3dB before processing. After recording, there should be no problem Maximizing the digital file to the default of 0dB (=1.0 =100%).

GoldWave (like most audio editors) uses floating-point internally, and it can temporarily go over 0dB without clipping/distorting. But, if you do any processing that might boost the levels (such as volume adjustments or EQ), it's a good idea to run Volume Maximize again as the last step before saving. Maximizing will bring the volume up or down as need for 0dB peaks. That will insure that your saved file is not clipped during saving...

Regular 8-bit and 16-bit WAV files are hard limited to 0dB and if you try to go over, you'll get clipping. Your analog-to-digital converter (recording) and your digital-to-analog converter (playback) is also hard-limited at 0dB.

I'm not sure if downsampling to 8-bits makes the distortion sound worse, but it might.

Quantization noise is MUCH worse at 8-bits than at 16-bits, but it should be more noticeable with quiet sounds than with loud sounds. (There is no quantization noise during dead-silence.)
But I found out that there is one single step in converting blasting the sound: 16-bit to 8-bit.
What is "blasting"?
It gives an unpleasant hiz in the output-file...

...Using the hiz-filter has litle effect
What's "hiz"? What's the "hiz filter"?
marera
Posts: 8
Joined: Tue Feb 02, 2016 9:47 am

Re: Converting 16-bit to 8-bit issue

Post by marera »

Hi folks,
thank you both for your detailed comments. I will try your hints later tody and report!

Excuse my poor english:
"hiz" should be "hiss". I applied the "hiss removal"-preset from the noise reduction filter (with no positive effect).

"blasting the sound": I meant "distorts the sound" (the step "converting 16-bit to 8-bit").

Marc
marera
Posts: 8
Joined: Tue Feb 02, 2016 9:47 am

Re: Converting 16-bit to 8-bit issue

Post by marera »

Here is what I tried, according to how I understand your hints:

The original file is 44KHz .m4a, peaks up to 0.6 on the y-axis in GW.

1st: saved as PCM signed 16-bit mono 44.1KHz

2nd: resampled to 22.050KHz

3rd: maximised volume to 100%

4th: saved as PCM unsigned 8bit mono, 22KHz

The result is about as poor as in my first attempts. Maybe I simply expect too much from the 8-bit file?!
marera
Posts: 8
Joined: Tue Feb 02, 2016 9:47 am

Re: Converting 16-bit to 8-bit issue

Post by marera »

I uploaded the original file and my result to zeta-upload, maybe you'd like to have a look at it:

https://www.zeta-uploader.com/829533700

https://www.zeta-uploader.com/1649080183

Larger file is 325KB.
DougDbug
Posts: 2172
Joined: Wed Feb 16, 2005 3:33 pm
Location: Silicon Valley

Re: Converting 16-bit to 8-bit issue

Post by DougDbug »

Just to let you know, I'm at work right now and I can't listen to your file (or do any experiments) until I get home this evening (California time).

The hiss is probably quantization noise. If so, we can't eliminate it. :
( Sometimes people are able to reduce the hiss with noise reduction, but then it comes back when they re-save at 8-bits.

The might be something we can do with dynamic compression (The Compressor/Expander effect). Dynamic compression (not related to file compression like MP3 or MP4) can be used to bring-up the quieter sounds without boosting/clipping the peaks. That should bring-up the overall/average volume and it should improve the signal-to-noise ratio.

There is another "trick" I want to try too...
2leftfeet
Posts: 149
Joined: Sun Jan 20, 2013 10:28 pm
Location: Napier New Zealand

Re: Converting 16-bit to 8-bit issue

Post by 2leftfeet »

Hello again,
If you listen carefully to the clip you can hear some low level noise in the quiet parts, especially in the first second. There is also a click in there. You need to get rid of the click and then the low level noise in the entire track. This is how I did it:-

In the original file delete the click at 0.536 to 0.538 seconds.
Now select the track from 0.0 to 0.8 seconds and copy this section to the clipboard.
Now highlight the whole track and go to the noise reduction and in the “reduction envelope” check the “Use Clipboard” box. In the “Settings”, select FFT 12, Overlap 8X and Scale 100. Now hit OK. The last thing is to maximise the volume (I suggest 90%).

Save the audio clip at the required setting and there you are! It is certainly better.
I have uploaded my attempt to Wikisend.

Go to http://wikisend.com and download the file number 457850
DougDbug
Posts: 2172
Joined: Wed Feb 16, 2005 3:33 pm
Location: Silicon Valley

Re: Converting 16-bit to 8-bit issue

Post by DougDbug »

I agree with 2leftfeet... You need to reduce the existing noise before downsampling to 8-bits. As I was saying, quantization noise is worse at low volumes (except where you have dead-silence), and where you have existing low-level noise, the quantization noise is ADDED to the existing noise.

Here are a couple more things to try -

1. High pass filter. Effect -> Filter -> Low/Highpass. Set to 40Hz and highpass.
That won't affect the sound, but it will help to even-out the positive & negative peaks which will get the file slightly louder when you maximize later. (And the louder the file, the better the signal-to-noise ratio.)

2. Try a noisegate. A noisegate kills (or reduces) the background noise when the sound falls below a preset threshold (such as when there is only noise). But it can sound unnatural, so try it to see if it makes things better or worse. Effect -> Compressor/Expander -> Noise gate 3 preset. (You should probably Maximize volume before doing this.)

3. Try some compression. This is a 3-step process...
- Effect -> Volume -> Maximize Volume
- Effect -> Compressor/Expander -> Reduce Peaks preset
- Effect -> Volume -> Maximize Volume

Again, the idea of this 3-step compression is to make the file louder for a better signal-to-noise ratio when you downsample to 8-bits.) And, note that compression will increase the existing background noise, so you'll what to use noise reduction (and/or the noisegate) before compression.
2leftfeet
Posts: 149
Joined: Sun Jan 20, 2013 10:28 pm
Location: Napier New Zealand

Re: Converting 16-bit to 8-bit issue

Post by 2leftfeet »

Maybe we are not thinking straight here - DougDbug has more good ideas to try, but how about opening a new sound file with a sample rate of 22050 which you close & save straight away with 8 bit mono attributes. Now open it again and record your message. Check it for levels, pops, clicks etc., I am thinking that this method is modifying the audio more than necessary. When you have to edit then downsample an existing signal you are degrading the original each time you make a change to it. Each time you alter the sample rate you add quantizing noise to it. By starting with an empty audio track with the wanted parameters, you are removing one step in the process. Having said that, you are never going to get amazing quality with such a low sample & bitrate anyway. This might work for you, give it a go!
marera
Posts: 8
Joined: Tue Feb 02, 2016 9:47 am

Re: Converting 16-bit to 8-bit issue

Post by marera »

Good morning (at least in germany...)!

I really appreciate all you eger and effort your are taking in my task!

I shall try all your suggestions later today, maybe only next week. I Shall report as soon as I'll have news for you!
Recording in the target format is a good idea certainly, but: I receive the file from a studio, and they just don't do it...
Recording myself is not an option, for I havn't got a good mic (only the notebook built-in one), and my voice sounds not as pleasant as my client expects the voice to be.
Maybe I should try to place a nice girl on my lap while speaking, that should make my voice sound deeper, smoother, fuller, more pleasant. I'll give it a try!
2leftfeet
Posts: 149
Joined: Sun Jan 20, 2013 10:28 pm
Location: Napier New Zealand

Re: Converting 16-bit to 8-bit issue

Post by 2leftfeet »

I have a German friend here in New Zealand. He is used to talking into microphones (his daughters or wife might be willing as well) would not mind doing a recording if all else fails - I have good mikes, etc but we shall see!
Cheers Peter.
marera
Posts: 8
Joined: Tue Feb 02, 2016 9:47 am

Re: Converting 16-bit to 8-bit issue

Post by marera »

Hi Peter,

that's a great offer! But before getting a whloe bunch of your friends at work, could you possibly do a little test?
Just record a few words a you suggested by yourself, to see if the result is worth it?

Thanks a lot!

Where are your german friends from in germany, the accents, you know....?

BTW: It's amazing having experts from Canada and New Zeeland supporting me in Germany, init?
2leftfeet
Posts: 149
Joined: Sun Jan 20, 2013 10:28 pm
Location: Napier New Zealand

Re: Converting 16-bit to 8-bit issue

Post by 2leftfeet »

My friend comes from the Beriln area & now lives here. He travels all over the world for his work so might have to wait a little. I will try out a test in a day or two like you suggest and let you know how I get on.
marera
Posts: 8
Joined: Tue Feb 02, 2016 9:47 am

Re: Converting 16-bit to 8-bit issue

Post by marera »

Great! In case we (actually you) find out, that recording in 8-bit is the right way, I maybe would buy a mike and give it a try on my own. It's already a lot I ask of you...
Anyway I'll try DougDbugs suggestions netxt week, you are not forgotten!
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