Audacity Forum

Audacity 2.1.1
Windows 7

Someone said on this forum that if you convert 128 kbps to 128 kbps, it will effectively cut the quality in half to 64. Is there any conversion loss table that shows what the loss would be with other combinations? I commonly save 192 from mp4 to 320.

Xerlome wrote:Someone said on this forum that if you convert 128 kbps to 128 kbps, it will effectively cut the quality in half to 64.

That sounds like an exaggeration, though there will be some loss of sound quality.

Xerlome wrote:Is there any conversion loss table that shows what the loss would be with other combinations? I

"Quality" is highly subjective, and among other things, it depends on the type of material being encoded. For a listener, orchestral music is more likely to show the effects of MP3 compression than say generated test tones, but it may be easier to measure the loss in the generated test tones than in the orchestral music.

High bit-rates will preserve the sound quality better than low bit-rates, and "lossless" formats (such as WAV and FLAC) are best of all, but at the end of the day it is your ears that are the only judge.

That's an approximation. It could happen. It's the illustration of why it's a terrible idea to do production in MP3 or any other compression format. Successful modern compression algorithms can pay attention to content and it's not simple to publish a conversion table.

As a fuzzy approximation, pick the midpoint between the two compression rates and take half.

There are rules of thumb.

You should take the AudioBook compression values of 192 Minimum at their word. If you can get your chapters to fit in their other requirements at higher compression, do it. The ACX post-production products will come out better and more reliable the higher you go.

You get another significant quality improvement if you submit mono instead of stereo.

Koz

It's true if you stick to the higher compression rates, you can go a very long time before you experience any audible damage at all. But. Post production or other unexpected sound management can just kill you.

There is a poster who was doing a show for a small local radio station. To cut a long story, they couldn't make an MP3 podcast of his show because the MP3 music he used turned to bubbly trash.

Oopsie.

Do all your work in WAV and only convert to compression if you're reasonably sure it's the final product. I have one personal recorder with no provision to record at perfect quality WAV. It's in a box somewhere in the bottom of my desk. It's pretty to look at.

Koz

from mp4 to 320.

It's my understanding that MP4/AAC was designed to be "more immune" to re-compression damage than MP3.

Depending on what kind of editing you're doing, there are special-purpose editors that can edit compressed files without decompressing/re-compressing. mp3DirectCut works with MP3 and AAC files.

And there's another super fuzzy minimum rule. Right around 32, most people can just start to hear some sound damage in a mono show if they're not exposed to the original work. 64 for Stereo. The transitions are pretty steep. Lower than 32, Mono sound turns to garbage immediately. Above 32 the damage becomes very much less apparent. Audacity stereo MP3 default export used to be 128 which is "safe."

But not safe for production. Safe to listen to with little or no apparent damage.

Compressed formats in production are a land mine. Nobody knows it's there until Blammo!

"My show sounds like a bad cellphone when I made the MP3 to upload...."

Koz

Thanks for the thoughtful replies. I understand the advice to use lossless, but that isn't practical or even possible in this situation, I use 192 kbps audio I extract from the standard HD online music video (720p) using Audacity. I save it at 320 kbps and that is what goes on the air. I have good reason to believe that the 192 is made directly from original commercial quality audio. The station equipment does not support WAV, and for prerecorded shows, the program manager doesn't want enormous files like WAV. I need to investigate the other lossless types. The sound I get from the mp3 is good enough, though probably could be better. The questionable part is whether it retains fidelity after conversion to the station's 128 stream. So the specific question is whether the 320 from 192 would technically (leaving subjectively aside) be reduced below the 128 quality capacity of the stream, or (I'm hoping) be higher than the 128 stream can communicate, thus be as good as it can be. The "fuzzy approximation" would make it 128. This is assuming "all other factors being equal", meaning that I am actually getting good 192, and not just 192 made from trash. I may be the local programmer you mentioned, Kos. But the station management never complained about my audio, it is I who am so determined to do it the best way possible. To do my shows, which features the lesser known, I must use online, because the station library doesn't have most of what I need, and I can't afford thousands of CDs. Hopefully, the artists are happy for the exposure. Anything you think I could do better, under the circumstances?

I need to investigate the other lossless types.

It wouldn't take much investigation. FLAC as I understand it is the only zero-damage compressed format.

Delivery improvement is one option, but there is a way to get better music.

The iTunes store offers higher price music ($1.29 up from the famous 99c) which has much higher compression quality and no FairPlay copy-guard.
So no, you don't have to invest hundreds in a CD collection. you can do reasonable quality one $1.29 song at a time.

Koz

I will look into whether FLAC will work on our equipment. Even if it does, if FLAC is a very large file like WAV, that can also be an issue. What is the smallest lossless type? The mp3DirectCut looks interesting, although I don't understand it. It will do things Audacity won't do?

As a programmer, I cannot afford to buy the music I use. $0.99 or $1.29 adds up fast, thousands of dollars per year it would be. I need to collect several times as much as I use in order to have the selection options on hand for immediate review or use, because it is not practical (or even possible) to recall and chase down each item online at the time I need it. Much of what I need is international or otherwise obscure, and not available through the usual commercial sources. Although I am not a commercial promoter, what I do is effectively free promotion. The station subscribes to a system which pays the royalties for what we play.

Xerlome wrote:What is the smallest lossless type?

Most lossless compressed formats (including FLAC) reduce the file size to about 50 to 60% of the original uncompressed size. I don't know of any lossless formats that do better than that.