How To Give Yourself A Stereo Check-Out - London

 

How To Give Yourself A Stereo Check-Out

How To Give Yourself A Stereo Check-Out

Commentary spoken by Jack De Manio and Elizabeth Knight

London Records PS 523

1967

From the back cover: The equipment used by the professional recording engineer for making recordings, and playing them back, is constantly checked and rechecked, the purpose being to reduce unwanted noise, distortion and other undesirable defects whilst at the same time ensuring the maximum fidelity of sound. The measuring instruments used in this evaluation process are costly and involved.

THE AIM OF THIS RECORD is to provide a means for the demanding listener to check record playing equipment without the need for such expensive and complicated instruments. With care it can remain a lasting tool, the standard of which will not change with time, whereas the equipment itself – and indeed the human ear – must certainly alter with age. 

All of the tests contained in this record are inter-dependant, and it is therefore suggested that it be played through once completely before attempting to interpret the results which may be obtained from it. It is emphasized also that the purpose of records and record reproducing equipment is to give pleasure and even with the finest of equipment some degree of compromise will always be necessary.

Side One

Band1

A short INTRODUCTION to explain the purpose of this record to the listener.

Band 2
LEFT-RIGHT CHANNEL IDENTIFICATION, LOUDSPEAKER BALANCE AND CHANNEL PHASING.

When a recording is made a very exact balance is engineered between the sounds coming from the extreme left and right- hand sides of the sound stage, and also the sounds that are located between them. By ensuring that the channels are correctly identified and the loudspeakers balanced for volume you will be listening from a centre seat in the stalls instead of from the wings or even back-stage!

To simplify these tests, two voices in varying positions are used. When necessary a metronome is added as this too is easily located.

Incorrect channel phasing can result in a loss of low frequencies and produce a sound that is thin and pinched. It also makes the location of centre sound images very difficult.

To illustrate these effects, two voices are again used – one in phase, and the other out of phase.

The human voice, containing many frequencies including "highs" on sibilants, and the metronome, having a steep wave front occupying as it does a short time interval, make them particularly easy to locate as sources of sound.

Band 3
MONOPHONIC MUSIC
This is included as a further check for loudspeaker balance and phasing and should be heard coming from a point mid-way between your loudspeakers.

(It should be noted that monophonic music played over two speakers creates a slightly broader sound image than a single voice which as explained above is particularly critical in pin-pointing the location of sound).

Band 4
TONE CONTROLS
Most amplifier tone controls affect the extreme high and low frequencies, leaving the mid-frequencies relatively unaffected. To help you set these in a position that is correct for your loudspeakers and your own ears, listen carefully to the high, mid, and low frequency warble tones recorded in this band. By varying the tone controls until the high and low frequencies sound as loud as the mid-frequency, or pilot tone, you will have equalized the frequency response of your amplifier to suit your own listening conditions. By the way, a warble tone is a tone, the frequency of which is continuously varying within fixed limits. It is used in this section because, unlike a pure tone, it will not reflect from the plain surfaces within your listening room and produce varying intensities of sound a phenomenon known as "standing waves".

Band 5
SOUND COLOURATION
Different positions of your loudspeakers within the listening room in which they are located can often produce quite different results in sound. This can either be attributed to the loudspeakers themselves or resonances within the listening room. By listening to pink noise divided into small sections of the audio range (see under) and comparing these sections against a pilot tone in the mid-frequency range, any variations in loudness can easily be heard. If these variations are very audible, re-positioning of the speakers may give a more even response. Sound colouration is caused by uneven frequency response and is usually unfavourable to realism.

*Pink noise contains all the frequencies in the audio range and is a modified form of white noise. White noise contains all frequencies including those beyond the audible range. The third octave sections of pink noise used are heard in the following order:

16 KHZ           630 Hz
10                    400
6.3                   250

4.0                   160
2.5                   100
1.6                     63
1.0 (pilot tone)    40

Band 6

STEREOPHONIC MUSIC
The musical instruments featured in this recording produce sounds extending from the very lowest frequency to the highest, whilst the intensity of sound from each instrument compared to the others represents a very wide dynamic range. Because of this, they are amongst those most hazardous to a recording engineer. The faithful reproduction of their sounds presents similar hazards.

Band 7
GROOVE-JUMPING AND DISTORTION.
Two of the contributory factors to groove-jumping and distortion are

i) the pickup cartridge itself may have insufficient compliance (which means that the reproducing point is not sufficiently free to move), and

ii) the recorded level on the record may be too high, causing severe excursions within the groove which the cartridge cannot follow.

Four musical instruments have been recorded at three different levels for comparison purposes. You will be able to detect any distortion or indications of groove-jumping in your equipment as the levels increase. The highest level in each case is similar to that found on the majority of quality records.

Band 8
SILENT GROOVES

The purpose of this band is to detect how much rumble and hum is present when you play a record.

For checking rumble, play a few silent grooves and then, by lifting the cartridge upwards from the record, note any decrease in the low frequency noise that rumble produces. For hum, play a few silent grooves and again make a comparison by lifting the cartridge off the surface of the record. Any hum remaining may emanate from your amplifier, but it may come from the motor driving the turntable. To check the latter, move the arm laterally towards its rest and listen for any alteration of hum. Hum usually produces a slightly higher and harder sound than rumble.

Side 2

Band 1

LIVE VERSUS RECORDED SOUND

To carry out this test, the following objects should be to hand:

Matches, a bunch of keys, a newspaper, carving knife and steel, a paper-bag, an unopened bottle of wine and glass, balloons, a pair of scissors and paper, feathers.

One of the problems with even the best equipment is to determine how natural the reproduced sound is. For this purpose a series of sounds, using objects which can be found in most homes have been recorded. Each sound is followed by a few seconds of silent groove. The listener, by using similar objects, can then compare the live versus the recorded sound. For an accurate comparison the listener should ensure that the volume of the recorded sound is the same as the sound he makes.

Band 2
WOW AND FLUTTER
This is probably the most difficult test given you on this record, but the presence of wow and/or flutter can influence the sound from a record in a very unpleasant manner, and therefore their elimination is highly desirable. Wow and flutter, (which the commentary defines for you) are best assessed by listening to the single tone at three thousand cycles per second (3 KHz). This should be heard as a perfectly steady tone without variations in pitch. To avoid any problems of standing waves which may give rise to confusion, the listener is recommended to stand close to one speaker.

Band 3
ANTI-SKATING BAND
Friction between the reproducing point and the surface of the record produces a force which makes the cartridge arm try to swing toward the record centre, and because of this the stylus tends to remain in closer contact with one side of the groove than the other. This can give excessive emphasis to one channel, producing stereo mis-balance, and will result in undue wear of the groove wall. To overcome this undesir able effect, some arms are fitted with a bias, or anti-skating, adjuster. If the arm is over-compensated it will, of course, tend to skate toward the outer edge of the record.

Place the pick-up cartridge stylus mid-way in the wide ungrooved area of this record whilst the record is turning. If the arm is correctly adjusted there should be no tendency for the arm to "skate" either toward the centre of the record or toward the outer edge.

(If your cartridge arm has no bias compensator we advise you not to try this test, but proceed to band 4).

Band 4
CROSSTALK
This is the break-through of sound from one channel to the other, which results in a reduction in the width of the sound stage which ideally extends fully from one speaker to the other.

Crosstalk occurs within a pick-up cartridge and its associate amplifier, and varies at different points within the frequency spectrum. Therefore for this test a musical composition is used, specially arranged for a group of instruments which covers this full frequency range. This music, recorded in one channel only, while the other channel is "silent", affords the opportunity to assess the degree of separation. 

Band 5

AN EXTRACT FROM HARY JANOS (Kodály)
Istvan Kertesz conducting the LSO.

This piece of music, by virtue of its composition and orchestration will help you finally assess your record playing equipment for most of the factors previously under test.

In listening the following test in particular should be recalled:

Location of sound (Side 1, band 2); Colouration of sound (Side 1, band 5); Dynamic range (Side 1, band 6); Distortion (Side 1, band 7); Realism; (Side 2, band 1)