Goldline Music 10 Real Time Spectrum Analyser
The purpose of a spectrum analyser is to pinpoint non-linearities in the frequency response of an audio system caused by system inadequacies, speaker placement, or room acoustics, so that a degree of corrective equalisation may be applied.
The usual method of performing this analysis is to inject white or pink noise into the system and then analyse the acoustic energy picked up via a flat response microphone.
Analysis is then achieved by passing the received signal through a set of bandpass filters and examining the signal level in each frequency band.
Pink noise contains an equal amount of energy in every octave and is generally preferred for this type of measurement. White noise contains an equal amount of energy in each cycle (frequency) and, consequently, the high frequencies will contain much more energy than the low ones as there are fewer cycles per octave for the lower frequencies.
As well as having an unnatural frequency distribution, white noise can very easily burn out tweeters due to its high HF (high frequency) content.
The Music 10 uses pink noise and the analysis is displayed by means of ten rows of nine LEDs which indicate the sound energy in octave bands from 31Hz to 16kHz.
Each band reads between +3dB and -20dB, and a gain control is fitted so that any reasonable signal level may be accommodated.
The Music 10 is a self-contained, hand held unit which contains the noise source, the microphone and the analyser, and may be powered by means of internal batteries or a mains adaptor. The case is moulded from black plastic and closely resembles one of those Star Trek devices that they point and say 'No sign of intelligent life here captain!'
A red plastic screen covers the LEDs and an edge-operated control allows the gain to be adjusted smoothly.
Apart from the inevitable on/off switch there is a three position switch which selects fast or slow decay time for the display, or enables the display to be held indefinitely for further examination.
The pink noise output is available via a standard quarter inch jack socket, whilst a mini jack provides a line input so that off-tape signals, for example, may be checked for flat response.
An omnidirectional electret microphone is fitted at the front end of the analyser, positioned to avoid shielding effects from the case, and this is mounted behind a screen to minimise the risk of physical damage.
Connecting the pink noise output into a good quality domestic hi-fi yielded interesting results. Switching on the analyser, the gain was adjusted so that the LED columns reached approximately the 0dB line and the first noticeable thing was that they did not read very steadily, moving up and down by two or three dB's.
A certain amount of high frequency roll-off is to be expected in larger room's and this is indicated by a guideline on the display. It was difficult to read the constantly moving display but it became evident that at least one prominent peak around 2kHz existed at my listening position, due mainly I think to the speaker positioning, and my proximity to a wall.
Moving the analyser only slightly, yielded different results, underlining the importance of positioning.
The 'hold' mode freezes the current display, but as the readings fluctuate, this does not give a true indication of what is happening. Using the slow decay switch setting gives a slightly better display, but the integration time is still not long enough to obtain conclusively steady results.
The unit is priced at £249 and this is probably a reasonable price for the technology involved. I would, however, suggest that ten bands is not really enough for serious control room equalisation work and the positioning of the unit does appear to have a dramatic effect on its readout.
One area in which this device would probably be worthwhile is in mobile PA applications, where gross anomalies could be located and dealt with fairly efficiently.
Frequencies likely to give feedback problems can also be identified and the instruction sheet gives practical advice in this direction as well as suggestions for checking tape recorder head alignment.
It is unlikely that the small studio or home recordist would make sufficient use of this instrument to justify buying it, and a fully professional studio would undoubtedly hire something more sophisticated for the short time that it would be required.
With a bit of practice, I'm sure that this analyser is capable of giving valuable indications of what is wrong in a given acoustic environment but for my money, I think that the guy with the mobile PA rig is going to be the biggest potential customer.
Further details from Marquee Electronics Ltd., (Contact Details).
Review by Paul White
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