Saving as an MP3, Attributes

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kodiak4012000
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Saving as an MP3, Attributes

Post by kodiak4012000 »

There are a lot of choices for "ACM," "hz" and "kbps." :shock: How do I choose which one? :? Music vs Speech What effect will my choice have for file size and sound quality?

DewDude420
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Post by DewDude420 »

ACM is Audio Compression Manager, they are the codecs built in to Windows vs the external LAME codec which generally provides better quality.

HZ is the sampling rate the encoder will use. Naturally, the higher the number the better the quality, but the bitrate requirements will increase.

kbps is the bitrate, it is how many bits a second the mp3 file will be. the higher the number, the higher the number the more data that will be used to store the audio. more data means better quality.

music is a more complex wave than voice, therefore it will require more data to accurately reproduce. voice is a rather simple wave that you can get away with using less data and even a lower sampling rate, since the human voice doesn't require the entire human range to reproduce accurately.

a good standard to look at is 22khz 64kbps for voice (although you can go with lower if you like) and 44khz 192kbps for music (higher is better)

DougDbug
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Post by DougDbug »

There are lots of LAME options & settings, but once you find the settings that work for you, you can set-up a preset. It's always hard to answer these questions because some people are looking for the best possible quality, some people are looking for the smallest possible files, and some people (perhaps most people) are looking for a compromise. Personally, I'm not too concerned with disk space, so I use a high-quality setting (VBR 0), and then I don't worry about it.

Plus, some people can hear artifacts (MP3 distortions) that other people cannot, and some music (or voice) is more difficult to compress than than other sounds.... You might find that most of your music sounds perfect at 192kbps, but a few songs have artifacts at that bitrate.

Sample Rate (Hz or kHz):
In general, keep the same sample rate as the original. There is no advantage in increasing the sample rate more than the original. Decreasing the sample rate limits the high frequencies, so with music you shouldn't decrease the sample rate.

And, I wouldn't generally recommend decreasing the sample rate with voice either. It's something you can try if you are trying to squeeze the files as much as possible... You might get better sound at low bitrates if you force a low sample rate. But MP3 is pretty smart, so most of the time you don't have to "force" anything.

The sample rate applies to both compressed and uncompressed audio. There is an little introduction to digital audio on the Audacity Web Site, and it shows how "samples" are taken to digitize a wave. (i.e. 44,100 samples per second.)

Bit Rate (kbps):
As you probably know, MP3 is lossy compression. More data is thrown-away at lower bitrates:
Higher bitrate = higher quality = bigger file size = lower compression.

Lower bitrate = lower quality = smaller file size = higher compression.
The LAME encoder has Variable Rit Rate (VBR) which is usually the best option... With VBR, you select the quality you want (V0=best, V9=worst), and LAME chooses the bitrate for you, and it adjusts the bitate moment-to-moment depending on the sound content for the best overall compromise. (GoldWave allows you to set a bitrate range along with VBR, and it's generally best to set a wide range, and allow LAME to do the "thinking" for you.)

You can calculate the bitrate for uncompressed files (from the sample rate and the bit depth), but we usually only talk about bitrate with compressed files.

If you have a stereo file, Joint Stereo is usually the best choice. Again, LAME will analyze the content and give you the best quality for any given bitrate/quality setting.

Hydrogenaudio.org has lots of information and recommended LAME settings for different situations. The people at Hydrogenaudio, are generally looking for the lowest bitrate (smallest file) for "transparent" encoding, where the MP3 will sound identical to the uncompressed original.

If you're concerned with getting the best audio quality, Hydrogenaudio also has information on blind ABX testing so you can compare your MP3 to the original and confirm that you can't hear a difference between the MP3 and the original in a blind test.

Kummel
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Post by Kummel »

Concerning the VBR, some players can have problem to estimate the timing of the file.
:D

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