Noise with very low sound music

[Trebor]

Trebor, why did you say that the signal to noise ratio is lower? When we decrease the signal amplitude by using compressor/amplify/envelope tool I thought the noise was also decreased , thus keeping the ration constant. No?

There is usually a constant "Noise floor”, ( * see quantization noise and dither noise)

I’d just like to concur with bgravato and Steve: I too can’t hear any obvious hiss in the “low level” recording (before I amplified it).

* you could try "exporting" (saving) your Audacity files in 32-bit depth WAV format to avoid this constant but minute noise, if you've got plenty memory.

Dither [noise] is only applied when converting from a higher bit depth to a lower bit depth. Exporting to WAV or other uncompressed audio format is virtually lossless in all situations. However there may be a very small amount of change to the audio data with some types of uncompressed audio export, depending on the settings in Audacity Preferences (see below).

Exporting to 32-bit PCM WAV format is 100% lossless - no dithering is applied.
Exporting to 24-bit PCM WAV format may be dithered with a peak dither level of around -130 dB
Exporting to 16-bit PCM WAV format may be dithered with a peak dither level of around -80 dB

http://wiki.audacityteam.org/wiki/Dither

[steve]

* you could try "exporting" (saving) your Audacity files in 32-bit depth WAV format to avoid this constant but minute noise, if you've got plenty memory.

That is the ONLY way to avoid adding distortion and/or noise.

After amplifying the audio down by 28 dB or so, 16-bit formats do not have enough data for very low amplitude sounds, so you can use dither and introduce a little noise, or not use dither and introduce a different kind of (worse) noise and distortion.

However, as this is for a Podcast, I presume that the final destination format is MP3. You cannot get as good quality sound with MP3 encoding as with 32-bit (float) uncompressed audio. The sound quality that you are currently achieving is about as good as you will get with MP3.

[Soldado266]

Found out what the problem was.
I got my whole family involved on this. Two cousins of mine who are musicians got into a very hard discussion about that noise. One could hear the noise, and the other couldn't. After testing the mp3 files on all the computers (using the same headset) I found out that the problems is within the computers somehow.
There must be some problem with my computer sound card.

Just for the record... I use an Acer aspire5735, if somebody else has a similar problem using a similar computer this might be the answer.

This might be consider out of the topic, but is that a common problem? I mean, do usually built in laptop sound cards have such an influence on the audio quality?

Thanks

[bgravato]

Built-in soundcards usually are not very good on quality... Mostly because they usually have very poor shielding, which means you'll get a lot of electromagnetic interference from the other computer components inside the computer case.

As an example, when I bought a new bigger and more powerful graphics card to my desktop computer, it's fan was sitting pretty close to the "sound path" to the front panel headphones output of the built-in sound card. When I connected my headphones there I could hear what sounded like if a chopper was flying around inside the computer case. I then bought an Asus Xonar Essence STX, which is a "audiophile" sound card which very good shielding and good components and filtering. I can now hear bearly noise-free sound from my computer. In an addition to all that, also the quality of the DAC (digital to analog converter) will have influence on the quality of the outputted sound regardless of all added interferences.

On another example... I also have a macbook pro laptop. I also own a few good pairs of headphones, different types, shapes, brands, impedences, etc... I've tried them all on the mac and while I can get good sound out of all those headphones, out of my cd player in the living the room, when I connect my headphones to the laptop some of them will give me much more noise than others. I found the best for the mac was a cheap pair of Sennheiser PX100. I also have a radiopaq jazz IEM which sound great on my mp3 player and on the cd player, but they sound terrible on the mac... lots of hiss/white noise. That to say that sometimes it's not just one compenent alone that makes it bad, but can also be the combination of two components who together don't play well...

[steve]

The on-board sound card in my laptop is rubbish. Playback is not too bad, but the recording quality is terrible. Consequently, I use a Behringer UCA 202 USB sound card and the audio quality is very much better (line-in recording and line out only).