/*Dictionary of Terms*/

Frequency Response

Test Level Out 1kHz

Noise

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Electret Microphone

An electret microphone is a type of a condenser microphone (or pressure mic) that uses a diaphragm between a fixed internal volume of air and the environment. It responds uniformly to pressure from all directions and is said to be omni-directional. An electret mic's diaphram is made from a permanently-charged material which eliminates the need for a polarizing power supply (phantom power).

Omni-directional

Capable of receiving sound waves from all directions. An omnidirectional microphone's response is sphereical in three dimensions.

The wavelength of sound at 10 kHz is little over an inch (3.4 cm). The smallest measuring microphones are often 1/4" (6 mm) (the Lindos MM4 mic is 7mm) in diameter, which practically eliminates directionality even up to the highest audible frequencies. Omnidirectional microphones, unlike cardioids, do not employ resonant cavities as delays, and so can be considered the "purest" microphones in terms of low coloration; they add very little to the original sound. Being pressure-sensitive they can also have a very flat low-frequency response down to 20 Hz or below. Pressure-sensitive microphones also respond much less to wind noise and plosives than directional (velocity sensitive) microphones.

How we worked out this optimum spacing

The human ear interprets time differences between the two ears and uses them to locate low frequency sounds, up to 700Hz. Above 700Hz the phase information becomes increasingly unreliable and at 1kHz the brain relies entirely on level differences for positioning cues. For accurate phase capture the time delay must be smaller than the wavelength of the highest frequency you wish to reproduce stereo positioning for. For 1kHz the maximum delay between the channels is 1.0ms or (35cm in air).

Colouration

If the sound from a microphone sounds different in some way to the original it is said to sound coloured. A microphone that has low colouration means that it adds very little to the original sound.

Cardioid

Cardioid refers to a microphone with a heart-shaped polar response pattern. This is achieved using a diaphragm that is partially open at the front and partially closed on the back. The pressure difference between the two sides produces its directional characteristics, but as each frequency is effected differently the result is coloured to some degree.

Frequency response

Frequency response is a specification used to indicate how uniformly a piece of equipment receives or reproduces sounds from the lowest tones to the highest tones. A child is capable of hearing frequencies from 20Hz to 20kHz, as we age our ears response to high frequencies decreases.

Clipping

Clipping occurs when a system is overloaded. In the case of a preamplifier, if the gain control is set too high then as the input increases the output level will stop increasing in line with the input level. The output will sound increasingly distorted as the preamp becomes more overloaded.

European Broadcasting Union

The European Broadcasting Union is a confederation of broadcasting organisations from around the world. Its members are mostly radio and television companies which it supports by encouraging cooperation on technical issues to facilitate programme interchange and common working practices.


v5.6

New waveforms for negative going sawtooths & double tones (providing OSC13 EPROMs or later are fitted); difference frequency distortion measurement (see below); support for LA103 Insertion Test Unit if detected; double width printing problem fixed (introduced in V5.5); automatic distortion option selection improved; limited support for CCITT O.33 FSK headers in both LA101 and LA102; remote keyboard support added; minor bug fixes.

Segment V (400Hz test level) no longer forces 400Hz normalisation of the frequency response graph, since this can now be achieved by using LA102 configuration J, or by using a tolerance definition to force the normalisation frequency, and it was felt to be confusing having three different ways of doing it. For users who still want a sequence to force 400Hz normalisation it is possible to add a ‘±21’ to the end of the sequence, to make it
select tolerance 21 which in turn forces 400Hz normalisation. Sawtooth waveform IMD measurement replaced by Difference Frequency Distortion measurement, which gives a result 3dB lower. This is in accordance with the IEC268-3 specification which uses a different reference level.

The NA? remote command provisionally introduced in V5.0 software has been dropped. Similarly, the Softstrip results printout which was in earlier software is
no longer available, as we know of nobody still using this feature. Intermodulation distortion V5.6 software can generate a 1kHz double tone with 70Hz separation for difference frequency distortion measurement, and a new segment (d) has been provided to measure this. However, the LA101 also requires the latest (OSC13) waveform EPROMs in order to generate the double tone. New units supplied with V5.6 or later software will be fitted with these waveform EPROMs, but users upgrading older units who wish to use this feature should request new waveform EPROMs from Lindos. To find whether a unit has OSC13 EPROMs, press [*][4] to step through the waveforms and look for DOUBLE (or remove the bottom cover and check the label on the EPROMs).New waveforms for negative going sawtooths & double tones (providing OSC13 EPROMs or later are fitted); difference frequency distortion measurement (see below); support for LA103 Insertion Test Unit if detected; double width printing problem fixed (introduced in V5.5); automatic distortion option selection improved; limited support for CCITT O.33 FSK headers in both LA101 and LA102; remote keyboard support added; minor bug fixes.

Segment V (400Hz test level) no longer forces 400Hz normalisation of the frequency response graph, since this can now be achieved by using LA102 configuration J, or by using a tolerance definition to force the normalisation frequency (section 5.4), and it was felt to be confusing having three different ways of doing it. For users who still want a sequence to force 400Hz normalisation it is possible to add a ‘±21’ to the end of the sequence, to make it select tolerance 21 which in turn forces 400Hz normalisation. Sawtooth waveform IMD measurement replaced by Difference Frequency Distortion measurement, which gives a result 3dB lower. This is in accordance with the IEC268-3 specification which uses a different reference level.

The NA? remote command provisionally introduced in V5.0 software has been dropped. Similarly, the Softstrip results printout which was in earlier software is
no longer available, as we know of nobody still using this feature. intermodulation distortion V5.6 software can generate a 1kHz double tone with 70Hz separation for difference frequency distortion measurement, and a new segment (d) has been provided to measure this. However, the LA101 also requires the latest (OSC13) waveform EPROMs in order to generate the double tone. New units supplied with V5.6 or later software will be fitted with these waveform EPROMs, but users upgrading older units who wish to use this feature should request new waveform EPROMs from Lindos. To find whether a unit has OSC13 EPROMs, press [*][4] to step through the waveforms and look for DOUBLE (or remove the bottom cover and check the label on the EPROMs).