Bit Depth and Bit Rate

If you have worked with digital audio a bit you have probably heard the terms bit depth and bitrate. Bit depth is the number of pieces of information recorded for each sample of audio. (Wikipedia). CD-quality audio is recorded at 16 bits, which corresponds to 44.1 kHz. DVD-quality audio can  be recorded at up to 24 bits. A larger bit depth results in a more accurate conversion from analog sound. Bitrate is the amount of data needed to transmit an audio file. 16/44 audio is roughly 1.4 Mbps (megabits per second).

audio bit depth


White Noise, Pink Noise, Brown Noise

The subject of today’s post is three kinds of noise you can generate easily in Audacity or a similar program: white noise, pink noise, and brown noise. Everyone has heard of white noise. White noise is a combination of all audible audio frequencies. It is often used in the production of electronic music because it can cut through all other audio frequencies. The sirens on some emergency vehicles use white noise because it can be heard over background noise, making these vehicles easier to locate.

You may not have heard of pink noise. It drops off by 3 dB per octave as frequencies climb, with equal amplitude across each wave. Since lower frequencies have more power than higher frequencies, pink noise sounds more like a roar than a hiss. It is sometimes generated by analog synthesizers. Brown noise is also referred to as Brownian noise and red noise. The term “brown” comes from Brownian motion and does not refer to the color brown. Robert Brown discovered Brownian motion.  It decreases in amplitude by 6 dB for as frequencies increase, resulting in a heavy bass sound.

The table below is a graphical representation of these three kinds of noise, which I generated in Audacity.

white noise, pink noise, and brown noise generated by Audacity

Auto Duck

Auto Duck

Well, the holidays are over and I hope all of you had a great time. With this post I hope to get back on my schedule of posting an update every week. Consider this scenario: you have found some great background music you want to use for the introduction (intro) and the ending of your podcast (outro). You would like to have the music play for a few seconds at the beginning, gradually fade out as you begin speaking, and fade back in at the ending. How can we do this if it is even possible?

The answer is the auto duck feature found in Garageband, Audacity, and some other audio programs. It is very easy to do in Audacity. First, place the background track on top and the spoken podcast track underneath it. Select the background track and press Effect > Auto Duck. Audacity automatically creates a fast fade-out and a gradual fade-in. That’s all there is to it.