Acoustic Feedback is most often experienced as the nasty screeching you sometimes hear coming out of speakers at a concert, or when someone is talking over a public address system. It is a high pitched sound that rises quickly to a shriek – and is not only unpleasant to hear, it can be downright dangerous for your equipment. Feedback is also known as howlround.
Feedback is produced when an unwanted sound output (or audio signal) from a loudspeaker or audio device is fed back to an earlier part of the sound reproduction system. The unwanted audio signal is picked up and amplified (made louder) by the electronic circuits in the system. The amplified sound is then output again over the speakers, and is picked up again by the inputs (microphone), making a closed loop. The system then quickly becomes overloaded, and this is heard as a nasty screeching sound through the loudspeakers.
Typically, feedback happens when the speakers in a public address system are placed behind the microphone, giving the speaker output a chance to go back to the input and be amplified. To stop feedback, you have to break the feedback loop. In the example described above, you will have to move the mic to a place where sound coming from the speakers is not picked up by the mic. Or you can move the loudspeakers so that their output cannot reach the mic. Moving either the speakers or the mic will break the feedback loop, and the system will work properly.
Avoid situations that will lead to acoustic feedback for two reasons: Firstly, it always affects your sound output. The noise is horrible and it will make your sound unlistenable. Even a small amount of feedback can cause echoes or boosting or cutting of certain frequencies.
Secondly the very high signal levels associated with feedback can destroy or damage loudspeakers and other equipment that are part of the feedback loop. Acoustic feedback is not acceptable at all in the broadcast studio. To make sure feedback from the mic to the loudspeakers doesn’t happen, broadcast studios have special switching units. These units, often incorporated into the mixer, turn off the studio loudspeakers whenever a microphone is turned on. The same switching unit also normally triggers the RAG lights or On-air lights. These are indicator lights placed inside and outside the studio to show that a microphone is switched on, and that someone is ON AIR. It is good practice never to enter or leave the studio when the on-air light is on. Another kind of in-studio feedback relates to recording equipment. For example, let us assume a recording device is being used to record a signal from the recording output of a mixing desk. If the recorder’s output is added to the mix on the mixer’s recording bus, and you lift the fader of the channel feeding the recorder, feedback will occur. The audio is feeding back into the system, and the same kind of noise will result.
1. Cassette recorders
Cassette recorders are the most common field recording devices available in many places even today. The cassettes that we use in them are readily available almost everywhere, and are quite cheap. They are relatively rugged, easy to repair – cassette recorders are plentiful enough for even the average electronics repairmen to fix the common problems – and are relatively cheap. Good cassette field recorder models are the Sony Recording Walkman series, and (a little more expensive, but with far more controls for professional grade work) the Sony TCD-5M recorders.
2. Minidisc recorders
The minidisc or MD was originally invented by Sony as a replacement for its cassette walkman players – that is, as a handy portable recorder that could carry high quality audio. It never found acceptance in the home consumer market, as it was an expensive device. Instead, it became popular with filmmakers and journalists as a way to record high quality digital stereo audio. MDs have been the staple recorder for a number of CR stations across the globe for some time. The newer Sony HiMD models – an upgraded version with higher capacity media and the ability to record PCM WAV uncompressed audio – are still quite popular. The recorders are priced quite reasonably for the quality of recording; and the HiMD recorders offer the additional option of digital USB transfers for editing on a DAW, making them an attractive option.
3. Flash recorders
The most recent type of field recorder – and by far the ones gaining greatest ground today - are the solid state flash recorders that record on Compact Flash (CF) media or Secure Digital (SD) cards. As digital memory has improved in tandem with the increasing roles computers play in our lives, flash recorders – which use the same kind of solid state memory used in computer BIOS memory – have also improved by leaps and bounds. The most recent versions – like Zoom’s H-2 recorder or the Edirol R-09 – are very high quality instruments, with the ability to record several hours of high quality audio on media that are rapidly becoming cheaper by the day. (SD cards are available in 8 GB versions today, enough for over 10 hours of non stop recording in uncompressed WAV format; and CF cards are available in as high a capacity as 64GB.)
Feedback is produced when an unwanted sound output (or audio signal) from a loudspeaker or audio device is fed back to an earlier part of the sound reproduction system. The unwanted audio signal is picked up and amplified (made louder) by the electronic circuits in the system. The amplified sound is then output again over the speakers, and is picked up again by the inputs (microphone), making a closed loop. The system then quickly becomes overloaded, and this is heard as a nasty screeching sound through the loudspeakers.
Typically, feedback happens when the speakers in a public address system are placed behind the microphone, giving the speaker output a chance to go back to the input and be amplified. To stop feedback, you have to break the feedback loop. In the example described above, you will have to move the mic to a place where sound coming from the speakers is not picked up by the mic. Or you can move the loudspeakers so that their output cannot reach the mic. Moving either the speakers or the mic will break the feedback loop, and the system will work properly.
Secondly the very high signal levels associated with feedback can destroy or damage loudspeakers and other equipment that are part of the feedback loop. Acoustic feedback is not acceptable at all in the broadcast studio. To make sure feedback from the mic to the loudspeakers doesn’t happen, broadcast studios have special switching units. These units, often incorporated into the mixer, turn off the studio loudspeakers whenever a microphone is turned on. The same switching unit also normally triggers the RAG lights or On-air lights. These are indicator lights placed inside and outside the studio to show that a microphone is switched on, and that someone is ON AIR. It is good practice never to enter or leave the studio when the on-air light is on. Another kind of in-studio feedback relates to recording equipment. For example, let us assume a recording device is being used to record a signal from the recording output of a mixing desk. If the recorder’s output is added to the mix on the mixer’s recording bus, and you lift the fader of the channel feeding the recorder, feedback will occur. The audio is feeding back into the system, and the same kind of noise will result.
FIELD RECORDERS
The term field recorder refers to any portable recording device that allows reporters to go into the field with the means to capture sound. Because there are so many different kinds of field recorders you can buy, it is impossible to enumerate every type that is available in the market. But we can quickly list the most popular varieties.1. Cassette recorders
Cassette recorders are the most common field recording devices available in many places even today. The cassettes that we use in them are readily available almost everywhere, and are quite cheap. They are relatively rugged, easy to repair – cassette recorders are plentiful enough for even the average electronics repairmen to fix the common problems – and are relatively cheap. Good cassette field recorder models are the Sony Recording Walkman series, and (a little more expensive, but with far more controls for professional grade work) the Sony TCD-5M recorders.
2. Minidisc recorders
The minidisc or MD was originally invented by Sony as a replacement for its cassette walkman players – that is, as a handy portable recorder that could carry high quality audio. It never found acceptance in the home consumer market, as it was an expensive device. Instead, it became popular with filmmakers and journalists as a way to record high quality digital stereo audio. MDs have been the staple recorder for a number of CR stations across the globe for some time. The newer Sony HiMD models – an upgraded version with higher capacity media and the ability to record PCM WAV uncompressed audio – are still quite popular. The recorders are priced quite reasonably for the quality of recording; and the HiMD recorders offer the additional option of digital USB transfers for editing on a DAW, making them an attractive option.
3. Flash recorders
The most recent type of field recorder – and by far the ones gaining greatest ground today - are the solid state flash recorders that record on Compact Flash (CF) media or Secure Digital (SD) cards. As digital memory has improved in tandem with the increasing roles computers play in our lives, flash recorders – which use the same kind of solid state memory used in computer BIOS memory – have also improved by leaps and bounds. The most recent versions – like Zoom’s H-2 recorder or the Edirol R-09 – are very high quality instruments, with the ability to record several hours of high quality audio on media that are rapidly becoming cheaper by the day. (SD cards are available in 8 GB versions today, enough for over 10 hours of non stop recording in uncompressed WAV format; and CF cards are available in as high a capacity as 64GB.)
Conducting a field recording
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