Audio Recording

If you find yourself confused how much dB to cut or boost in your audio mastering for bass level, then this tutorial provide some tips. This will be using Adobe Audition 1.5, although if you are using other audio mastering software you can as well apply the concepts illustrated here provided the feature that is needed in the analysis is supported by your software. Supposing you are working on a mix down file in 24-bit/96KHz WAV for mastering; you listen to it and find out that the bass is too strong. Or in the opposite it might be too weak. Again, it depends on the material. One of the techniques is to have a reference track that is already mastered with the desired bass level. You have select this reference track or in some cases provided by your client as an example. Of course, you can always adjust your EQ for the bass frequencies (below 200Hz) up or down and then match the level with your reference if you are working in a very accurate monitoring environment. But this is a subjective approach. It works well for me. But if you like both subjective and objective approach, the following are the steps:

1.) You need to make the average SPL level of the reference track to be same average SPL level with your mix down file. In Adobe Audition, open the reference track first in the Editor view. Go to Analyze – Statistics. Supposing you’ve got the result below for the average SPL level:

Left Right
Average RMS Power: -13.82 dB -13.93 dB
Using RMS Window of 50 ms

Take the average of the left and right channel, so it’s about -13.875dB.

2.) Now close this reference track and then open your mix down file (to be mastered) and go to Analyze – Statistics. Supposing you have the results below:

Left Right
Average RMS Power: -17.16 dB -16.79 dB
Using RMS Window of 50 ms

Take the average of the left and right average RMS power. So it’s about -16.975dB.

3.) You have noticed that the reference track is obviously louder (because its already mastered). Take their difference:

Difference = -13.875dB-(-16.975dB) = 3.1dB

You need to basically apply a 3.1dB reduction on the reference mastered track so that it will have the same average SPL level with your mix down file.

4.) Now re-open the reference mastered track in Adobe Audition editor view and then go to Effects – Amplitude – Amplify/Fade. Under Presets, select -3dB cut; in the box, change -3dB to the actual value to be applied which is -3.1dB. Click OK to proceed. See screenshot below:

5.) After implementing a -3.1dB reduction on the reference track. It will have a similar SPL level with the mix down file you are working. Similar SPL is important in making unbiased comparisons. If you are comparing the frequency response of two waveforms with different SPL then it’s not an accurate comparison. The next thing you should do is to analyze the bass level of the reference track using frequency spectrum analyzer. This is basically a Fast Fourier transform analysis to view the frequency spectrum. Open the reference track in Adobe Audition Editor View. Go to Edit then “Select Entire Wave”; then go to Analyze – Show Frequency Analysis. Select the maximum FFT size which is 65536 Blackmann-Harris. Then click Scan; wait until it will be completed (for both LEFT and RIGHT channels). Below is the resulting screenshot of the frequency analysis of the reference track:

6.) Now do the same for your mix down. Analyze the frequency response using Frequency Analysis tool (same maximum FFT size and Blackmann-Harris). Supposing you got the results below:

Analysis:

Its clear where in the specific bass frequency region needs adjustment; the sub-bass regions (40Hz and below) seem to have similar level with the reference track. It is because they are both at the comparable level of -48dB so it’s OK. Take note that in the frequency analysis, the x-axis is the frequency while the y-axis the amplitude in dB. Next the 50Hz region for both reference and mix down track are also comparable (-36dB) so it does not need EQ adjustment. There is only one bass region in the mix down wav file that needs significant adjustment:

1.) 100Hz region – the mix down level is around -36dB while the reference track is around -30dB; this implies that the track you are mastering (the mix down file) lacks 100Hz bass.

Recommendations:

Simply use parametric EQ and start to apply a +6dB boost on 100Hz Q=1.4 or 2.0 on your mix down file. Use your ear to re-confirm the EQ adjustment. If you compare both reference track and the track you are working with; you should see a big improvement in the bass level and it should now be pretty comparable. Work on getting balance, if you boosted the bass this can affect also the mid-range to high frequencies. In this case, you need to perform analysis in those frequency bands also using similar technique.