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Audio Frequency

Identify the first low frequency audio filter?

Can anyone date and briefly describe the first low frequency audio filter. It was effective below 500 Hz with limited enhancment of higher audio frequencies.
No I'm refering to a filter which eliminated audio below 500Hz. To add a bit more. It was almost created by accident and the 500Hz was arbitrary. i.e. not done through knowledge of impediance or reactance.
It was the feature of an ancient theater with a seating capacity of 14,000. The perfect accoustics has baffled experts for years and only recently explained by an engineer.

The filter effect erased background noise, while the brain processed the missing sound along with the higher frequencis so no content was lost. I believe it's called phantom audio.

Did you mean amplifier?

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Voice Frequency $68.51 High Quality Content by WIKIPEDIA articles A voice frequency (VF) or voice band is one of the frequencies, within part of the audio range, that is used for the transmission of speech. In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz. It is for this reason that the ultra low frequency band of the electromagnetic spectrum between 300 and 3000 Hz is also referred to as voice frequency (despite the fact that this is electromagnetic energy, not acoustic energy). The bandwidth allocated for a single voicefrequency transmission channel is usually 4 kHz, including guard bands, allowing a sampling rate of 8 kHz to be used as the basis of the pulse code modulation system used for the digital PSTN. Author: Surhone, Lambert M./ Timpledon, Miriam T./ Marseken, Susan F. Binding Type: Paperback Number of Pages: 76 Publication Date: 2010/07/04 Language: English Dimensions: 5.98 x 9.01 x 0.18 inches

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The SteelSeries 7H features 50mm drivers with a remarkably wide frequency response that delivers rich and detailed audio reprod $150.12 The SteelSeries 7H features 50mm drivers with a remarkably wide frequency response that delivers rich and detailed audio reprod

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Audio frequency range of LP vs. CD



Is there a unit that can be used to block out all audio frequencies apart from vocal/voice frequencies?

I need a unit to be able to only allow the vocal frequencies to be heard through the speaker after using a microphone to pick up the original audio. This is a microphone used in a busy and noisy machine workshop so the speaker that will play the audio live will only allow the vocal/voice frequency to be heard and not the noise from machinery.

Is there anything like this that exists?

You need to install a low-pass and a high pass filter.

the low pass should be set to roughly 3KHz and the high pass should be set to 200Hz.

this means that all signals above 200Hz pass through the High pass and all the signals less than 3Khz pass through the low pass giving you a band of 2800Hz.

This may be too large for effective noise reduction in your instance so you would have to narrow the band. I have heard that 200Hz-1200Hz comes through clearly but sounds a little muffled.

Alternatively you could create a filter that blocks out only the frequencies of the machine noise. You would have to measure which frequencies have the highest amplitude (loudest) that come off of the machines. then you only allow frequencies that are on either side. This would require 2 speakers and 2 sets of filters. One for the high side and one for the low side of the blocked band of frequencies.

Electronic filters are really easy to make. They are a capacitor and resistor. The values of them determine the frequencies that are allowed to contiue along a circuit. You will need to either create one, or buy one.

hope this helps, I don't have time to go into more detail.

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