Audacity Forum

I have a podcast that has a very low volume. Is there a way using audacity to increase the volume of the mp3 track?

Thanks in advance.

argalorn wrote:I have a podcast that has a very low volume. Is there a way using audacity to increase the volume of the mp3 track?

You can use Effect > Amplify but this will bring up the surface noise. It would have been better if the person recording the podcast had recorded it higher so that it reached fairly close to top and bottom of the waveform.




Gale

When using the amplifty effect, amplify to a bit less than 0.0dB to avoid clipping (-1.0dB should be safe, -2.0dB will be safer)

bgravato wrote:When using the amplifty effect, amplify to a bit less than 0.0dB to avoid clipping (-1.0dB should be safe, -2.0dB will be safer)

If I'm following, I think the reason for this is that MP3 is a lossy "psycho-acoustical" encoding (it selects the audio to retain on the basis of it being the most perceptible). So (in Audacity, anyway, but less so in some other software), the actual peak amplitude of the exported MP3 may exceed what it is in the waveform after Amplify.

If that's the reasoning, this should be a negligible problem at higher MP3 export bit rates, but could be a problem at Audacity's default 128 kbps bit rate.




Gale

Gale Andrews wrote:

bgravato wrote:When using the amplifty effect, amplify to a bit less than 0.0dB to avoid clipping (-1.0dB should be safe, -2.0dB will be safer)

If I'm following, I think the reason for this is that MP3 is a lossy "psycho-acoustical" encoding (it selects the audio to retain on the basis of it being the most perceptible). So (in Audacity, anyway, but less so in some other software), the actual peak amplitude of the exported MP3 may exceed what it is in the waveform after Amplify.

If that's the reasoning, this should be a negligible problem at higher MP3 export bit rates, but could be a problem at Audacity's default 128 kbps bit rate.

Gale

The main reason I'd call it the "paranoid level" or something similar... Picking up a "real-world" analogy I'll compare it to cooking. When I make soup (my cooking specialty) I usually put less salt than what I should. The reason for this is that adding more salt later, if necessary, is much easier than removing the salt in excess...

bgravato wrote:

Gale Andrews wrote:

bgravato wrote:When using the amplifty effect, amplify to a bit less than 0.0dB to avoid clipping (-1.0dB should be safe, -2.0dB will be safer)

If I'm following, I think the reason for this is that MP3 is a lossy "psycho-acoustical" encoding (it selects the audio to retain on the basis of it being the most perceptible). So (in Audacity, anyway, but less so in some other software), the actual peak amplitude of the exported MP3 may exceed what it is in the waveform after Amplify.

The main reason I'd call it the "paranoid level" or something similar...

There shouldn't be any need for concern if exporting to WAV or AIFF though.



Gale

So I wonder: is there some minimum level that's acceptable? Obviously, on the back end you want to get as close to 0Db as you can without distorting, but if you do have a track that's too quiet and Amplifying means bringing in noise, what would be the minimum to amplify to?

Not that I think there's one standard out there, since it's likely dependent on the content of the track, but...

theseus75 wrote:So I wonder: is there some minimum level that's acceptable? Obviously, on the back end you want to get as close to 0Db as you can without distorting, but if you do have a track that's too quiet and Amplifying means bringing in noise, what would be the minimum to amplify to?

If you are recording, it is reasonable to aim to peak at -6 dB. Digital audio has a wide dynamic range between the noise level and the maximum signal level. Amplifying from -6 dB to 0 dB should not bring up noise noticeably, but it will avoid the risk of clipping above 0 dB, which means in most cases that the clipped audio will be damaged.

If you already have a recording at low amplitude, the signal to noise (SNR) ratio is lower, so amplifying it will make the noise louder as well as the signal. [However, as long as you work in Audacity's default 32-bit quality, amplifying won't make the SNR worse].

Only you can judge where the noise subjectively becomes too loud when you amplify, but you can try Effect > Noise Removal to attenuate noise (at the possible risk of introducing artifacts into the audio). If you are encoding to MP3, noise removal artifacts could become somewhat worse because MP3 is a lossy encoding.



Gale

I've shot for that (-6Db peak) in my last couple of recordings, and then used normalize to get up to around 0Db, and - indeed - I don't hear an increase in noise. I've still got lots of monkeying around with noise reduction to do, but that's for the tip on peak volume; seems to work well!

Just be aware that unlike the Amplify effect which works on the stereo pair as a pair - the Normalize effect works on each stereo channel independently. Useful if your setup is not balanced properly - but if it is, then you may end up changing/damaging the balance/stereo image.

For more detail see this discussion in the Wiki: http://wiki.audacityteam.org/wiki/Amplify_and_Normalize

WC