I have 2 questions, 1 on mp3 quality when opened in Audacity. 2. on using the limiter - pros and cons of input gain compared with make up gain.
I am transferring talks recorded on cassette to digital from a cassette player using line in, exporting audio and saving as mp3, then closing the Audacity file and not saving it.
If I reopen the mp3 with Audacity later to add effects like limiter or noise reduction, will I have lost the Audacity quality of sound - will the quality now only be mp3 or will it be Audacity quality because I’ve opened the mp3 with Audacity?
On using the Limiter: pros and cons of input gain compared with make up gain.
The tapes are hissy and while voice peaks are around -1 the lowest voice level is at times around -12. If I limit to about -3 and add input gain to bring up the low level, there is an increase in hiss and background noise. If I limit to about -3 and use make up gain instead of input gain which brings up the low level voice it seems a cleaner sound. However it peaks at 0.
I don’t know which is best- do you have any advice/tips?
I have also discovered that the lower the threshold set eg to -6 the higher are the make up gain peaks.
Don’t save your work-in-progress in MP3 format : the quality is degraded to some degree each time you save as mp3, the damage accumulates.
Use WAV or FLAC format instead, they are not lossy formats.
You can also save your work-in-progress as an Audacity project, which is loss-less.
Only use MP3 format for the final finished product, (if your customers insist on MP3).
If I reopen the mp3 with Audacity later to add effects like limiter or noise reduction, will I have lost the Audacity quality of sound - will the quality now only be mp3 or will it be Audacity quality because I’ve opened the mp3 with Audacity?
MP3 is lossy compression. Information is thrown-away during the compression process. Opening the file in Audacity is the same as playing it (it gets decompressed in both cases) and no further “damage” is done. However, if you re-export to MP3 you are going through a 2nd generation of lossy compression (sort-of like making a Xerox-of-a- Xerox.)
A good quality (high bitrate) MP3 can often sound identical to the uncompressed original, but it is lossy and the quality-loss accumulates with multiple generations of compression. So, if you want MP3, compress ONCE as the last step. Do your production, and save any intermediate files in a non-lossy format (WAV or as an AUP project is good). If you save-as an Audacity project (AUP), it’s a good idea to also export to WAV because an AUP project contains multiple files and sometimes “bad things” happen.
On using the Limiter: pros and cons of input gain compared with make up gain.
Input gain has a bigger effect on the limiting and character of the sound. Make-up gain just boosts the volume after limiting without changing the character of the sound.
Let’s say you limit to -1dB and most of the sound is less than -1dB and untouched by the limiting… Only the few peaks above -1dB will be limited. But if you use 1dB of input gain, any peaks that used to hit -1dB will now hit 0dB, and those peaks which wouldn’t have been touched before will now be limited (pushed-down).
there is an increase in hiss and background noise.
Anything you do to boost the levels, including Amplify, Input Gain or Make-up Gain will boost everything, including the background noise. Dynamic compression * and limiting reduce the peaks/louder parts, reducing dynamic range and making the signal-to-noise ratio WORSE.
FYI - A Noise Gate is a kind of downward expansion (the opposite of compression). But, a noise gate can often sound unnatural and it’s sometimes worse than the noise.
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Don’t confuse dynamic compression (compressor effect) with file compression (MP3). They are totally different concepts.