|
Why do we need a test disc and what’s an analyser?
We might think that we can tell when our audio system sounds good or not just by listening to our favourite music, and of course the most important thing is that we like what we hear when we play ‘our’ music - there’s no point aiming for some definitive audiophile sound if that’s not how we like it. But how do we know that it couldn’t be even better to our own ears than it is?
Let’s face it, unless you’re a recording engineer, your best reference is probably your own hi-fi system, or maybe your friend’s system. But that’s a kind of a loose reference. What you need is some way of comparing it to a real reference, and the best way to start is to have a CD that has been specially made to be a reference disc. It will have tracks that help to pinpoint things to listen for, and tracks specifically to help you set up equalisers and tone controls. You can play it on many different systems, including show cars with systems you can only dream of - then you’ll have a far better reference and a much better idea of where your own system scores or fails.
The SOUND CHECK 2 CD contains 99 tracks compiled by professional audio engineers Alan Parsons and Stephen Court and mastered at London's Abbey Road Studios. The disc has been designed not only to help assess the technical performance of audio equipment, but also to offer the best available musical, vocal and effects sources for system setup and demonstration.
It’s a terrific test disc, but what makes this package unique and perfect for the occasional setup and tweaking we do as car audio enthusiasts is that it includes, actually inside the double CD case, a built in microphone and sound level meter and all the required circuitry and power supply to give a self-contained, highly portable audio system analyser. It’s simple but it works and it’s very affordable.
Sound Check Response Analyser
Conventional spectrum analysis - often called Real Time Analysis or RTA - is used to measure an audio system's frequency response. This generally uses a pink noise signal covering the entire audio spectrum and an analyser that measures - in a single pass - the level of the signal at third octave points from 20Hz to 20kHz. It then plots all this and saves it in memory or prints it out for you as a frequency curve, showing where there are peaks and dips in the response.
A gradual lift in the bass end, for example, might well be desirable. What we don’t want to see are sudden changes between adjacent frequency bands because this will normally cause individual instruments and vocals to be reproduced in a way that was not intended by the musicians, recording engineer and record producer. In the worst cases it can result in an unnatural sound that’s tiring to listen to.
Conventional pro analysers take out the hard work by calculating the level of the pink noise at each third octave frequency point and then delivering the full frequency curve to us, all in one go. We have to set the microphone in the right position and set a few things on the machine, but it does just about all the hard work for us. The trouble is that they tend to be pretty expensive pieces of kit. If you are running a professional installation company then it’s usually worth the investment, but for enthusiasts it’s just too expensive. We just want something to help with the initial setting up and then occasional tweaking of the EQ. Having to pay out over a thousand pounds for an RTA just isn’t going to happen for most of us.
Computer-based software RTA’s can work well, but you still need a decent microphone, a laptop computer, the software and often an external sound card or module, because the built-in sound chips in most laptops are not designed for audio testing from 20Hz to 20kHz. Add the cost of that little lot up and it still makes you go “phew!”.
With the Sound Check Analyser and the Sound Check 2 CD, you can achieve an accurate full spectrum plot of your system’s frequency response curve for well under £100. It just takes a bit more effort - but not too much, once you get the hang of it.
The big difference, compared to a full function RTA, is that the measurements have to be taken at each third octave point one at a time. The level at each frequency point needs to be read from the built-in level meter and manually plotted onto a pre-prepared graph (a copy comes with the disc but you can download it from HERE and print out as many copies as you need). It takes a bit longer but it can be just as accurate in the end.
The Sound Check Analyser makes use of the individually recorded third octave bands on the CD. It simply steps through the third octave tones you need, one after the other. These are read by the integral sound pressure level meter calibrated in 3dB steps from -15dB to +12dB, with a central amber 0dB reference indication.
Most sound level meters are "weighted", or have a response curve tailored to approximate the human ear's response. The Sound Check Analyser uses an electret capacitor omnidirectional microphone with manufacturer's response specification of 20Hz - 20kHz +/-2dB. Therefore it is essentially flat. As "C" weighting is usually used for measuring music in professional circles, Sound Check's meter is calibrated to read approximately 80dBC at the 0dB reference point.
The third octave bands are warbled (modulated) to eliminate standing waves which could cause false readings, and the meter is averaged to provide steadier readings at low frequencies. As simple as it looks, this is a pro piece of test equipment.
|
