Community Media/MARAA/Community Radio/Production/What is Digital Audio
|Work in progress, expect frequent changes. Help and feedback is welcome. See discussion page.|
File formats of digital audio
Working with tape is easy, because you never have to think about what format of audio you are recording in. The physical form of tape took care of most things. Today after the computer has started being used, digital audio is the new accepted convention. Basically digital audio means that digital signals are being used to reproduce sound. This includes analog to digital conversion, digital to analog conversion, storage of audio, and transmission.The digital audio signal can be stored on a Compact Disc (CD), flash drive, mp3 player, hard drive or any other digital data storage device. Audio data compression techniques like mp3, Advanced Audio Coding (AAC), Ogg, Vorbis,Windows Media Audio or Flac are commonly used.
When you start thinking of digital audio, you will most probably think of mp3. Now, mp3 stands for MPEG-1 Audio Layer 3 which encodes audio using a form of lossy data compression. This means that basically the data is compressed and then decompressed. It is not the same as the original file but its close enough for you not to notice the difference! Approved as a standard in 1991, mp3 continues to be a globally compatible standard. MPEG stands for Moving Pictures Expert Group, a group which commonly sets standards for audio and video.
Of course the biggest advantage of using mp3 is the fact that it takes up very little space on the computer.
Exercise: Try recording a sound, using wav format, and then convert it to mp3 and notice the difference in file size. Try converting to mp3 using different bit rate settings
The other common format is the Windows Media Audio (WMA), which is a audio compression technique developed by Microsoft Corporation. It was primarily developed as a competitor to the popular mp3 format, which is highly popular.
Both mp3 and WMA are played by default on Windows Operating System.
Bit rate is proportional to the quality of sound. The higher the bit rate, the better the quality of sound.
Recording Digital Audio
You can record audio through mobile recorders and fixed recorders. A mobile recorder can be a flash recorder, mobile phone, mp3 player or even your laptop! A fixed recorder is a microphone attached to the mixing console or to your computer.
Exercise: Record sound using flash recorders and then record sound using studio microphone. Discuss differences in sound
Recording on Flash Recorders
This is an important aspect of community radio because a lot of times, community members will not have enough time or will be too far away to come to the studio to record audio. So many times, you will have to go to them and that means recording on the field. This way, flash recorders are very useful tools for reporters, and community radio producers. These are usually compact devices which record audio and store it in a digital format like mp3, or wma. The storage happens on internal memory chip or external memory card, which can be replaced when the recorder fills up. A headphone jack is provided for listening to levels of sound while recording, to listen to the recording after you've stopped, and to block out the outside ambient noise for the person who's recording! Usually all the sound recorders have an input jack for inserting an external microphones. Here is an example of an affordable digital sound recorder. Here is an example of an affordable external microphone for your recorder.
There are a wide variety of brands out there in the market. Ultimately, it is up to you to go out there, see what works for your specific needs, and then select the model which works for you best. Some of the better known flash recorders are Zoom, Sony, Olympus, Transcend etc.
Exercise: Record on flash recorders, try to record in different kinds of locations, noisy places, quiet places, at different distances, and at windy places. Discuss findings and share learning
Recording on Microphones
This usually takes place in the studio, where you are in complete control of sound level, you are not vulnerable to external conditions like ambiance, noise, wind etc. Here, more than external conditions, the kind of microphone assumes importance. Now there are many kinds of microphones. A broad classification of microphones is condenser and dynamic microphones.
Three important points to remember. One is that it produces very high quality sound due to it being very sensitive.
Second is that it requires a power source, usually from a mixer or batteries.
Third is that these microphones are expensive and are usually used inside the studio, where they are carefully taken care of and are less prone to damage.
Usually inexpensive, they are used for outside recording.
They are also usually moisture resistant.
Usually having a ribbon on the inside, these are tough microphones but are not the best recording devices when compared to condenser microphones.
SM-58 from Shure is one of the better known dynamic microphones.
Exercise: Try recording with both dynamic and condenser microphones, and compare differences. Discuss where each microphone can be used best.
Characteristics of Sound
Digital sound have some characteristics which are important to understand before you attempt to manipulate it. On most occasions, remember that although the sound you have on your recorder or computer is digital, the input is almost always analog. Therefore it is not the original sound, but a converted format of the source. Therefore try to ensure that the source is clean. The most common mistake is to assume that every kind of manipulation is possible using digital audio. If the disturbance is embedded in the original source of audio, then it is that much more work for you to clean up the audio. Digital audio is usually in the form of mono sound or stereo sound. Mono sound means that it is being reproduced in a single channel. The most common usage of mono sound is the voice you hear on the telephone. However, it is common to use stereo sound today in most cases. Stereo sound is sound being reproduced in two channels and is being used in most cases of FM broadcasts. However, it is not necessary to get into technical details of what are the differences between mono and stereo. The notable difference is when you have two speakers to play back the sound which is broadcast or recorded. It is a good practice to record sound on the computer using a stereo track, which makes the sound appear in two channels, left and right, which means for the left speaker and right speaker.
Path of Sound
To record in the studio, you need to understand how the sound travels within the studio, and the different hardware it encounters in that journey.
- The source speaks first in to the microphone
- From the microphone the sound travels all the way to the mixer, through the cables
- It reaches the mixer, where the volume, treble, bass etc is controlled, and from there it travels to the computer via another cable.
- Once it reaches the computer, it is registered on an external sound card, or on an in-built sound card, and then it goes on to the software.
- On the software, the same sound is registered as a wave, which you can see on your screen.
- Sound travels so quickly, that you are not aware of this journey, from the microphone to the computer, and this appears to be an instantaneous process.
- From your computer, the sound travels back to either monitoring speakers or computer speakers, and it is converted to analog sound, which is audible to the human ear.
Some tips of recording which are to be generally kept in mind will usually save you a lot of effort.
- Ensure that the person is talking in a quiet environment, without too much ambient noise.
- All cell phones close by to the source must be switched off, not just on Silent mode. The signals being received by the cell phone will be registered on the recorder
- If a person (s) is recording in the studio, tell them to remove the bangles, or any other personal accessories which are bound to make noise while recording.
- If you are recording and its windy outside, make sure to stand in such a way that your back is turned facing the direction of the wind. This way, your body will block out the wind as much as possible and will not affect the sound too much
- If your recorder does not show levels before recording, then do a small test recording by speaking into the microphone yourself. Listen to the levels, so you get an idea of where to place the microphone in terms of distance from source.
- If you are recording on the field, hold the microphone yourself, and don't hand it over to the source, because they might hold it too close or too far
- Use a pop filter for your microphone so that phonetic sounds like the letter P, don't cause disturbances.
- Notice the lines which are engraved on the end of the wire which is connected to the microphone, or which is there on your earphones. If there are two rings/bands, then it is going to record/playback on stereo, and if there is only one line, it is going to record/playback in mono.
- Before going out to record on the field, make sure you have spare batteries, enough free memory
- If you think that the sound you have recorded is bad, don't hesitate to ask the source to repeat the quote. It is always better to be safe than sorry.