Audio Recording

If you are doing self audio mastering at home for your own projects, you might wonder how to technically assess the readiness of your audio mastering output for broadcast applications.This is very important because a lot of home-made recordings are rejected at radio stations, TV stations, film projects etc because it does have a “broadcast quality recording”. Take for example an inquiry below from the reader of this website: thanks so much for your site…I was wondering if you could tell me the best equipment and volume levels to check a final mastered song to see if it’s ready…Like are cars best, home stereos or ipods? And at what volume levels? Loud as it will go and put that to the test for distortion and competition between vocals, music and drum?? Any hints would be awesome! thanks, essie. OK, since you have asked me what are the following technical/engineering check points that you would execute to say that the audio is “broadcast ready” , refer to the checkpoints below:

Checkpoint#1: Meeting the minimum technical audio requirement and specifications.

If you are testing audio for mastering quality, it needs to meet the minimum requirements for full testing:

1.) CD wav, 16-bit, 44.1Khz (of course during your mastering session; the bit depth should be higher e.g. at 24bits, 96Khz; it is finally dithered and downsampled to audio CD quality for testing and deployment purposes). It is recommended to only convert this to MP3 quality (for distribution for example) once your mastered track successfully passes all test.

2.) Before you do any dithering for 32bit/24bit to 16/44.1Khz conversion.You need to ensure that your audio filters most of the unwanted frequencies. If you examined most commercial releases, mastering engineers will apply a very sharp low pass filter at 16500Hz. This means the entire content above 16500Hz are severely attenuated by the filter. The purpose is that most hi-fi systems and even our human ear are only sensitive up to these frequency range level. The spectrum is conserved so that it won’t necessarily accumulate volumes for frequencies that are not so useful for reproduction. Below is a sample setting of a low pass filter executing a sharp filtering above 16500Hz and the resulting frequency spectrum of the audio wave:

Checkpoint#2: The average loudness of the track measured as average RMS power.

This is just a measurement of loudness for the track after mastering. The standard seems to be around -13dB to -11dB. Be careful not to be too loud except if you are joining the audio mastering loudness wars. You can use audio mastering software to measure the loudness. If you are using Adobe Audition, you can go to Analyze then click Statistics for the measurement of loudness. Below is a sample screenshot of the output:

Checkpoint#3: The subjective loudness as played by your studio monitors versus commercial reference audio of similar average RMS power.

In this checkpoint, what you will do is to play at a moderate volume your song after mastering and compare it with a reference song. It is important that both reference audio and your song must have the same or very similar average RMS power (e.g. -12dB). The main objective of doing this test is to detect mastering problems relating to adjusting the “presence” of your song. If the song is not optimally mastered for loudness, it may have high average RMS power (for example within -13dB to -11dB) however when it’s played along with a commercial reference track ,it sounds weak and inferior.If your song sounds weak despite having similar measurements of loudness, then you might need to remaster it by tweaking the “presence” frequencies in the EQ stage. These are commonly found within 500Hz to 4000Hz, the frequencies at which the human is most sensitive to change in loudness.

Checkpoint#4: Assessing tonal balance “flatness” by playing the song in different audio monitors and audio players

If the song manages to pass checkpoint #1 to #3. It is now the time to assess the flatness of your frequency range. The objective is that your mastered audio tonal quality should be consistent in different audio players and monitors.

1.) First, try playing this with your normal CD players and hi-fi monitors (do this outside your mastering studio). Insert commercial tracks in between your mastered audio test CD. Then try to play first at very loud volume. Make sure that the quality of your mastered track is consistent and does not output some distortions. Then switch to low volumes and make sure the quality is unaffected. If you seem to like the output of the mastered track using your favorite CD players, proceed to the next test.

2.) Try to play your mastered track in environment; for example using your friend CD players and monitors. Make sure the quality is consistent with the first test.

3.) Next is to play your track using headphones and using iPods for example. Check for noise and quality issues not detected using live monitors. If it passes this test, proceed to last test.

4.) Burn a CD along with commercial tracks and insert your mastered audio, play it along with your car stereo at both loud and soft volumes. Make sure you like the quality output of your mastered track. What happens next? If your mastered track passes the entire checkpoints then congratulations you just completed mastering the song and its now “broadcast ready”. It is now compatible with most audio players and monitors being used by music consumers. Often the most difficult is checkpoint #4. It is because the moment the mastered track is tested outside the mastering studio and it sounds awful then something is wrong with the room acoustics in the studio. Remastering should be done in a well balanced mastering studio so that EQ adjustments will not be erroneous.