Describing Sound - A Glossary - Page 15

Originally Posted by fordgtlover 

I think these might help. Unfortunately, both concepts are beyond the intent of this glossary - to describe sound.

 

 

http://en.wikipedia.org/wiki/Roll-off

http://en.wikipedia.org/wiki/Cut-off_frequency

 

Originally Posted by peaceful1 

 

 

I have stared at that link for 2 years but it's not that easy to understand 

one of my friends have send me a link :

http://www.integracoustics.com/MUG/MUG/bbs/stereophile_audio-glossary.html

the PDF version :

http://www.mediafire.com/?2k7f2pmq6vqpt18

answered lots of questions I had 

Originally Posted by gregorio 



I haven't read all of it but I found that article to be quite poor and high percentage of definitions were inaccurate.

Roll-Off is a term used in the application of audio filters. It is impossible to abruptly remove frequencies above or below a specified point (although in the digital domain we can create steeper filters with fewer artefacts than in the analogue domain). Filters work by reducing the amplitude (level) of frequencies above or below a certain point, the cut-off point. Say we have a HF filter (a Low Pass filter) and set the cut-off point at 2kHz and set the filter to -6dB per octave. The signal will start to be reduced from 2kHz (the cut-off frequency) at a rate that at 4kHz the level will be at -6dB, at 8kHz the level would be -12dB and at 16kHz the level would be -18dB. Filters are applied in 6dB poles, so a 3 pole filter would operate at -18dB per octave.

As an audio professional this has always been my understanding of roll-off and cut-off and is verified by the two wikipedia articles but does not agree with the inaccurate Stereophile definition.

G

Originally Posted by tranhieu 

That's a very informative input Gregorio. Apart from roll off is there any other inaccuratedefinitions? Thanks.

Originally Posted by gregorio 



I haven't read all of it but I found that article to be quite poor and high percentage of definitions were inaccurate.

Roll-Off is a term used in the application of audio filters. It is impossible to abruptly remove frequencies above or below a specified point (although in the digital domain we can create steeper filters with fewer artefacts than in the analogue domain). Filters work by reducing the amplitude (level) of frequencies above or below a certain point, the cut-off point. Say we have a HF filter (a Low Pass filter) and set the cut-off point at 2kHz and set the filter to -6dB per octave. The signal will start to be reduced from 2kHz (the cut-off frequency) at a rate that at 4kHz the level will be at -6dB, at 8kHz the level would be -12dB and at 16kHz the level would be -18dB. Filters are applied in 6dB poles, so a 3 pole filter would operate at -18dB per octave.

As an audio professional this has always been my understanding of roll-off and cut-off and is verified by the two wikipedia articles but does not agree with the inaccurate Stereophile definition.

G

Originally Posted by peaceful1 

Originally Posted by Gregorio 



There are a number of different places in the audio chain and reasons why filters are used. For example, they might be used in the recording chain to remove thumps or other unwanted sounds accidentally recorded or might be employed on certain channels (within the mix) for artistic reasons. Filters are used in some electronic circuits to restrict the audio frequencies which are allowed to pass through the circuit (to avoid distortion or other artefact's). Filters have to be employed in digital audio (AD Cs and DA Cs) to comply with the Nudist-Shannon Sampling Theorem (the scientific theorem upon which the existence of digital audio is based). Filters are found in transducers like microphones and speakers. And last but not least, the ear itself acts as a filter as well!

BTW, frequencies above 10kHz are not necessarily unpleasant.

G