JPS5931280B2 - Record for measuring distortion in multi-channel record playback system - Google Patents

Description

【発明の詳細な説明】 本発明はマルチチャンネルレコード再生系の歪測定用レ
コードに係り、マルチチャンネルレコード再生系のあら
ゆる原因による各種の歪を総合的に一度で測定でき、し
かも音楽による聴感の評価と良く一致する再生系の評価
を行ないうる歪測定用レコードを提供することを目的と
する。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a record for measuring distortion in a multi-channel record playback system, and is capable of comprehensively measuring various distortions caused by all causes of the multi-channel record playback system at once, and also enables evaluation of hearing sensation based on music. It is an object of the present invention to provide a distortion measurement record that can be used to evaluate a reproduction system that closely matches the above.

一般に、マルチチャンネルの各オーディオ信号を可聴周
波数帯域の直接波信号と所定周波数帯域の被角度変調波
信号とし、これら両信号の多重化信号が片チャンネルの
信号として１本の音溝の左右の壁に夫々切削録音されて
なるマルチチャンネルレコードは、その記録、再生過程
において種々の歪を発生することが知られている。Generally, each multi-channel audio signal is a direct wave signal in an audible frequency band and an angle-modulated wave signal in a predetermined frequency band, and a multiplexed signal of these two signals is used as a single channel signal on the left and right walls of a single sound groove. It is known that multi-channel records, which are cut and recorded individually, generate various distortions during the recording and playback process.

この歪には主として１変調歪（正しく変調されないため
の歪）２位相歪（側波帯の位相が合わないために生ずる
歪）、３振幅歪（側波帯の振幅関係がくずれたために生
ずる歪）、４干渉歪（クロストークにより他チーャンネ
ルの被角度変調波信号が干渉して生ずる歪）、５検波歪
（正しく検波されないための歪）等がある。その他にも
あるが、上記の各歪が殆どを占めると考えられる。マル
チチャンネルレコード再生の場合、上記各歪のうち特に
干渉歪が大で全体の５０％以上を占めている。そこで、
本出願人は先に特願昭４８−６１１０８号（特公昭５４
−２９０８１号公報）にて上記干渉歪の測定用レコード
を提案した。This distortion mainly includes 1-modulation distortion (distortion caused by incorrect modulation), 2-phase distortion (distortion caused by sidebands not being in phase), and 3-amplitude distortion (distortion caused by disruption of the amplitude relationship of sidebands). ), 4 interference distortion (distortion caused by interference of angle-modulated wave signals of other channels due to crosstalk), 5 detection distortion (distortion due to incorrect detection), etc. Although there are other distortions, it is thought that the above distortions account for most. In the case of multi-channel record playback, among the above distortions, interference distortion is particularly large, accounting for more than 50% of the total. Therefore,
The present applicant previously filed Japanese Patent Application No. 48-61108 (Japanese Patent Publication No. 54
-29081) proposed a record for measuring the above-mentioned interference distortion.

このレコードは、１００Ｈ２程度の低域周波数の単信号
で所定周波数の搬送波を所定変調度にて角度変調した信
号をその音溝の一方の壁に切削録音され、かつ対向チャ
ンネルに無変調キャリアが切削録音されている。単信号
を用いた理由は、測定が容易であり、かつ干渉歪がマル
チチャンネルレコード再生系における歪の殆どを占める
ということを考慮すれば＋分であると考えたからである
。また、１００Ｈｚ程度の低域周波数信号を用いた理由
は、次の通りである。すなわち、マルチチヤンネルレコ
ードシステムでは、周波数帯域を十分活用するため、例
えば約８００Ｈｚ以下では、周波数偏移が８００Ｈｚの
周波数変調方式をとつている。このため特に、１００Ｈ
ｚ程度以下の低域周波数帯域で変調指数が８以上となり
、このとき第７次以上の高調波の振幅が特に大となる。
一方マルチチヤンネルレコード再生系では７次から９次
までの高調波が検波出力において最も多く測定される。
従つて、１００Ｈｚ程度の低域周波数信号を用いること
により、歪の測定が容易となるからである。然るに、上
記提案になる測定用レコードは、その再生信号の歪の測
定による品質の評価と音楽による聴感の評価とが一致し
ない場合がしばしば発生するという問題点があつた。本
発明は上記問題点を解決するものであり、以下図面と共
にその１実施例につき説明する。This record is a single signal with a low frequency of about 100H2, in which a carrier wave of a predetermined frequency is angularly modulated with a predetermined degree of modulation, and is recorded by cutting into one wall of the sound groove, and an unmodulated carrier is cut into the opposite channel. It's being recorded. The reason for using a single signal is that it is easy to measure, and considering that interference distortion accounts for most of the distortion in a multi-channel record playback system, it is considered to be a plus. The reason for using a low frequency signal of about 100 Hz is as follows. That is, in order to make full use of the frequency band, the multi-channel record system uses a frequency modulation method with a frequency shift of 800 Hz, for example, below about 800 Hz. For this reason, especially 100H
The modulation index is 8 or more in a low frequency band below about z, and at this time, the amplitude of harmonics of the 7th order or higher becomes particularly large.
On the other hand, in a multi-channel record reproducing system, harmonics from the seventh to the ninth harmonics are most often measured in the detection output.
Therefore, by using a low frequency signal of about 100 Hz, distortion can be easily measured. However, the measurement record proposed above has a problem in that the quality evaluation based on the measurement of the distortion of the reproduced signal often does not match the audibility evaluation based on the music. The present invention solves the above problems, and one embodiment thereof will be described below with reference to the drawings.

本発明は次に述べる結果に基き、中域周波数（大略５０
０Ｈｚ〜３ｋＨｚ程度）と低域周波数（大略５０〜２０
０Ｈｚ程度）に各々相当する少なくとも２以上の第１及
び第２の単一周波数信号で所定周波数の搬送波を角度変
調し、この被角度変調波信号が被測定用信号として切削
録音されたレコードをマルチチヤンネルレコード再生系
の歪測定用に用いるようにしたものである。すなわち、
第１に上記提案になる測定レコードは、単音に近い音楽
では測定結果とその聴感の評価とが一致する。The present invention is based on the results described below, and is based on the results described below.
0Hz to 3kHz) and low frequency (approximately 50 to 20
A carrier wave of a predetermined frequency is angularly modulated with at least two or more first and second single frequency signals each corresponding to 0 Hz), and this angularly modulated wave signal is used as a signal to be measured when cutting and recording a record. It is designed to be used for measuring distortion in channel record playback systems. That is,
First, in the measurement record proposed above, for music that is close to single notes, the measurement results and the evaluation of the audibility match.

また第２にこの先の提案レコードは複雑な音楽では測定
結果とその聴感による評価とが―致しないことが多い。
第３に上記１００Ｈｚ程度の低域周波数信号に、例えば
約２ｋＨｚ程度の中域周波数信号を加え、この２信号で
搬送波を変調し、この復調信号を測定した結果、音楽の
聴感の評価と極めて良く一致した。第４に上記２信号で
変調された信号を復調すると、第１図に１で示す高調波
成分のみならず、２で示す混変調成分が多量に発生した
。ここで、同図中、ｆ１は約１００Ｈｚ，．ｆ２は約２
ｋＨｚの単一周波数の復調信号の周波数スベクトラムを
示す。そして第５に同一の上記２信号で変調された信号
を用いても、マルチチヤンネルレコード再生系によつて
は、第２図Ａ，Ｂに夫々示す如く、高調波成分Ｖ，ｌＩ
と混変調成分２１，７との割合が一定でなかつた。以上
５つの結果より、上記低域周波数の信号と混変調を発生
させ、この混変調が最も聴感にて感じ易い周波数（すな
わち、上記中．低域周波数）とすべく中域周波数の信号
を上記低域周波数の信号に加えた２信号で角度変調され
た被角度変調波信号を被測定用信号として用い、その高
調波や混変調歪を分析することにより、始めて音楽によ
る聴感の評価との一致が得られ、高調波歪のみあるいは
混変調歪のみを分析するだけでは音楽による聴感の評価
と十分な一致が得られないと結論される。なお、マルチ
チヤンネルレコードシステムにおいては、伝送されるべ
きチヤンネルの各無変調搬送波そのものは、位相が夫々
同期していることを前提として以下説明する。Secondly, in the proposed records, the measurement results and the aural evaluation often do not match when it comes to complex music.
Thirdly, we added a mid-range frequency signal of about 2 kHz to the above-mentioned low-frequency signal of about 100 Hz, modulated a carrier wave with these two signals, and measured the demodulated signal. The results showed that the results were very good in evaluating the audibility of music. Agreed. Fourthly, when the signal modulated by the above two signals was demodulated, not only harmonic components indicated by 1 in FIG. 1 but also a large amount of cross-modulation components indicated by 2 were generated. Here, in the figure, f1 is approximately 100Hz, . f2 is about 2
Figure 3 shows the frequency spectrum of a demodulated signal with a single frequency of kHz. Fifth, even if a signal modulated by the same two signals is used, depending on the multi-channel record playback system, harmonic components V, lI
and the cross-modulation components 21 and 7 were not constant. Based on the above five results, in order to generate cross-modulation with the above-mentioned low-frequency signal, and to set the frequency where this cross-modulation is most audibly perceptible (i.e., the above-mentioned middle and low-range frequencies), the mid-range frequency signal is By using an angle-modulated wave signal that has been angle-modulated with two signals added to a low-frequency signal as the signal to be measured, and analyzing its harmonics and cross-modulation distortion, we were able to match the evaluation of auditory sensation due to music for the first time. It is concluded that analyzing only harmonic distortion or cross-modulation distortion does not provide sufficient agreement with the evaluation of the auditory sense of music. In the multi-channel record system, the following description will be made on the premise that the phases of the unmodulated carrier waves of the channels to be transmitted are synchronized with each other.

第３図は本発明になるマルチチヤンネルレコード再生系
の歪測定用レコードの録音系の１実施例のプロツク系統
図を示す。FIG. 3 shows a block system diagram of one embodiment of a recording system for a record for measuring distortion in a multi-channel record playback system according to the present invention.

同図中、３は低域周波数発振器で、例えば約１００Ｈｚ
の第１の単一周波数信号を発振出力する。また、４は中
域周波数発振器で、例えば約２ｋＨｚの第２の単一周波
数信号を発振出力する。上記発振器３，４の各出力信号
は混合器５に夫々供給され、ここで混合された後、角度
変調器６に供給される。この角度変調器６よりマルチチ
ャンネルレコードに録音される被角度変調波信号の搬送
波中心周波数に等しい周波数（例えば３０ｋＨｚ）の無
変調キヤリアと、この３０ｋＨｚを上記２信号の重畳信
号で角度変調したマルチチヤンネルレコード再生系の被
角度変調波帯域内の周波数帯域を占有する第１の被角度
変調波信号とが取り出され、夫々混合器ｒに供給され、
ここで低域周波数発振器８よりの例えば約９０Ｈｚの信
号と多重される。これにより、混合器７の出力信号は、
第４図Ａに示す如く、約９０Ｈｚの信号１５と第１の被
角度変調波信号１７とよりなる周波数スベクトラムを有
し、出力端子１３よりカツタヘツド（図示せず）に測定
対象となるチヤンネル（左又は右）の被測定用信号とし
て供給される。これにより、この被測定用信号はレコー
ドの１本の音溝の左右の壁のいずれか一方の壁に切削録
音される。一方、中高域周波数発振器９より出力された
例えば約５ｋＨｚの第３の単一周波数信号は、角度変調
器１０に供給され、ここで例えば３０ｋＨｚの搬送波を
角度変調する。In the figure, 3 is a low frequency oscillator, for example about 100Hz.
oscillates and outputs a first single frequency signal. Further, 4 is a mid-range frequency oscillator which oscillates and outputs a second single frequency signal of approximately 2 kHz, for example. The output signals of the oscillators 3 and 4 are respectively supplied to a mixer 5, where they are mixed and then supplied to an angle modulator 6. An unmodulated carrier with a frequency (for example, 30 kHz) equal to the carrier wave center frequency of the angle-modulated wave signal recorded on a multi-channel record by the angle modulator 6, and a multi-channel in which this 30 kHz is angle-modulated with a superimposed signal of the above two signals. A first angle-modulated wave signal occupying a frequency band within the angle-modulated wave band of the record reproduction system is extracted and supplied to a mixer r, respectively;
Here, it is multiplexed with a signal of approximately 90 Hz from the low frequency oscillator 8, for example. As a result, the output signal of the mixer 7 is
As shown in FIG. 4A, it has a frequency spectrum consisting of a signal 15 of about 90 Hz and a first angle-modulated wave signal 17, and a channel to be measured (left (or right) is supplied as the signal under test. Thereby, this signal to be measured is cut and recorded on one of the left and right walls of one sound groove of the record. On the other hand, a third single frequency signal of approximately 5 kHz, for example, outputted from the mid-high frequency oscillator 9 is supplied to the angle modulator 10, where a carrier wave of, for example, 30 kHz is angle-modulated.

この角度変調器１０より取り出された第２の被角度変調
波信号は、混合器１１に供給され、ここで低域周波数発
振器１２よりの約１１０Ｈｚの信号と多重される。従つ
て、この混合器１１の出力信号は、第４図Ｂに示す如く
、約１１０Ｈｚの信号１８と第２の被角度変調波信号１
９とよりなる周波数スベクトラムを有し、出力端子１４
よりカツタヘツド（図示せず）に導かれる。これにより
、この信号は測定チヤンネルの反対のチヤンネルに、す
なわち、上記測定チャンネルの記録されている音溝の壁
とは反対側の壁に切削録音される。これにより（測定結
果をマルチチヤンネルレコードの再生音楽による聴感の
評価とより良く一致させることができる。第４図Ａ，Ｂ
に示す周波数スペクトラムの信号を記録されたレコード
をマルチチヤンネルレコード再生系にて再生し、被角度
変調波信号１７を復調して得られた２信号の高調波成分
、混変調成分を測定することにより、これら歪成分は該
マルチチヤンネルレコード再生系全体の全歪量として測
定され、音楽による聴感の評価とも良く対応する。The second angle-modulated wave signal extracted from the angle modulator 10 is supplied to a mixer 11, where it is multiplexed with a signal of approximately 110 Hz from a low frequency oscillator 12. Therefore, the output signal of this mixer 11 is composed of the approximately 110 Hz signal 18 and the second angle modulated wave signal 1, as shown in FIG. 4B.
9, and has a frequency spectrum consisting of 9 and an output terminal 14.
The cutter head (not shown) is guided by the cutter head (not shown). Thereby, this signal is cut and recorded in a channel opposite to the measurement channel, that is, on the wall of the measurement channel opposite to the wall of the recorded sound groove. As a result, it is possible to better match the measurement results with the evaluation of hearing sensation based on music played from multi-channel records. Fig. 4 A, B
By reproducing a record in which a signal with a frequency spectrum shown in is recorded using a multi-channel record reproducing system and demodulating the angle-modulated wave signal 17, the harmonic components and cross-modulation components of the two signals obtained are measured. These distortion components are measured as the total amount of distortion of the entire multi-channel record playback system, and correspond well to the evaluation of the auditory sense of music.

なお、可聴周波数帯域の信号として記録される上記約９
０Ｈｚ、１１０Ｈｚの低域周波数の信号は、特に大振幅
の信号とすることにより、ピツクアツブカートリツジの
針とび（正常なトレースを行なわない状態）等をも含め
て測定することができ、マルチチヤンネルレコード再生
系の歪測定用レコードとしてより測定範囲を拡大できる
。また、上記記録されるべきすべての信号周波数は、互
いに特殊な位相関係をもたせないよう、例えば数Ｈｚ程
度周波数をずらせるなどしてなるべく倍数関係とならな
いよう選定されている。（例えば前記２信号が正確な２
ｋＨｚと１００Ｈｚでは、丁度２０：１の倍数関係とな
り好ましくない）この周波数の選定により、あらゆる位
相関係の状態が一度に出現し、そのときの歪を測定する
ことができる。更に、測定結果を音楽による聴感の評価
により近付けるためには、上記変調信号数を３信号又は
それ以上に増せば良い。Note that the above-mentioned approximately 9 signals are recorded as signals in the audible frequency band.
By making the low frequency signals of 0Hz and 110Hz especially large amplitude signals, it is possible to measure things such as pick-up cartridge needle skipping (state where normal tracing is not performed), etc. The measurement range can be further expanded as a distortion measurement record for channel record playback systems. Further, all the signal frequencies to be recorded are selected so as not to have a special phase relationship with each other, for example, by shifting the frequencies by about several Hz, so as to avoid a multiple relationship as much as possible. (For example, if the two signals are accurate
(kHz and 100 Hz have a multiple relationship of exactly 20:1, which is undesirable) By selecting this frequency, states of all phase relationships appear at once, and the distortion at that time can be measured. Furthermore, in order to bring the measurement results closer to the evaluation of the auditory sense of music, the number of modulation signals may be increased to three or more.

但し、この場合は測定が複雑となり、それに見合う効果
はあまり期待できない。また更に、本発明は上記実施例
に限定されるものでほなく、測定チャンネルの可聴周波
数帯域には何も録音せずともよく、また非測定チヤンネ
ルは無変調搬送波そのものだけを録音するようにしても
よい。However, in this case, the measurement becomes complicated, and the effects commensurate with the complexity cannot be expected. Furthermore, the present invention is not limited to the above-mentioned embodiment, and it is not necessary to record anything in the audible frequency band of the measurement channel, and it is possible to record only the unmodulated carrier wave itself in the non-measurement channel. Good too.

上述の如く、本発明になるマルチチヤンネルレコード再
生系の歪測定用レコードぱ、低域周波数（５０〜２００
Ｈｚ程度）の１又は２以上の第１の単一周波数信号と、
中域周波数（５００Ｈｚ〜３ｋＨｚ程度）で、かつ、該
第１の単一周波数信号とは倍数関係にない周波数に選定
された１又は２以上の第２の単一周波数信号との重畳信
号で、所定周波数の搬送波を角度変調して得た、マルチ
チヤンネルレコード再生系の被角度変調波帯域内の周波
数帯域を占有する第１の被角度変調波信号又は該第１の
被角度変調波信号と上記低域周波数で、かっ、該第１の
単一周波数信号とは異なる一の信号との多重信号を被測
定チヤンネルの信号として１本の音溝の片方の壁に記録
され、かつ、該音溝の他方の壁には、該中域周波数より
も周波数が高い中高域周波数で、かつ、該第４及び第２
の単一周波数信号とは夫々倍数関係にない周波数に選定
された１又は２以上の第３の単一周波数信号で上記所定
周波数の搬送波を角度変調して得た第２の被角度変調波
信号と上記低域周波数で、かつ、該第３の単一周波数信
号とは異なる一の信号との多重信号、又は無変調搬送波
が記録されたレコードであつて、マルチチヤンネルレコ
ード再生系にて再生され、その再生信号の歪を測定する
ために用いられるようにしたため、多くの発振器を用い
ることなくこのレコードを再生するのみでマルチチャン
ネルレコード再生系のあらゆる原因による歪を総合的に
一度に測定でき、測定結果と音楽による聴感の評価との
対応を極めて良くでき、各種フイルタの組合せ、又はス
ベクトル分析器などの一般の測定器を組合せることによ
り、各種の測定ができ、しかも比較的容易にできる等の
数々の特長を有するものである。As mentioned above, the distortion measurement record of the multi-channel record playback system according to the present invention has a low frequency range (50 to 200).
one or more first single frequency signals on the order of Hz);
A superimposed signal with one or more second single frequency signals selected to have a mid-range frequency (approximately 500 Hz to 3 kHz) and a frequency that is not in a multiple relationship with the first single frequency signal, A first angle-modulated wave signal obtained by angle-modulating a carrier wave of a predetermined frequency and which occupies a frequency band within the angle-modulated wave band of a multi-channel record reproduction system, or the first angle-modulated wave signal and the above. At a low frequency, a multiplexed signal with a signal different from the first single frequency signal is recorded on one wall of one sound groove as a signal of the channel to be measured, and On the other wall of the fourth and second
A second angle-modulated wave signal obtained by angle-modulating the carrier wave of the predetermined frequency with one or more third single-frequency signals selected at frequencies that are not in a multiple relationship with the single-frequency signal. and a single signal different from the third single frequency signal at the above-mentioned low range frequency, or a record on which an unmodulated carrier wave is recorded, and which is reproduced by a multi-channel record reproduction system. Since it was designed to be used to measure the distortion of the reproduced signal, it is possible to comprehensively measure distortion caused by all causes in a multi-channel record playback system at once by simply playing this record without using many oscillators. The correspondence between the measurement results and the evaluation of hearing sensation based on music is extremely good, and various measurements can be made relatively easily by combining various filters or general measuring instruments such as spectral analyzers. It has many features such as.

【図面の簡単な説明】[Brief explanation of drawings]

第１図は本発明レコードの再生信号の歪の１例の分布を
示す周波数スベクトラム図、第２図Ａ，Ｂは夫々異なる
マルチチャンネルレコード再生系にて再生された２信号
変調波の歪分布の相違を示す周波数スベクトラム図、第
３図は本発明レコードの記録系の１実施例のブロツク系
統図、第Ａ図Ａ，Ｂは夫々本発明レコードに切削録音さ
れる測定チヤンネルの被測定用信号、非測定チヤンネル
の信号の１実施例の周波数スペクトラムを示す図である
。 １，１′，ｆ・・・・・・高調波成分、２，？，７・・
・・・・混変調成分、３，８，１２・・・・・・低域周
波数発振器、４゜゛゜“゜低域周波数発振器、６，１０
・・・・・・角度変調器、９・・・・・・中高域周波数
発振器。Figure 1 is a frequency vector diagram showing an example of the distribution of distortion in the reproduction signal of the record of the present invention, and Figures 2A and B are distortion distributions of two-signal modulated waves reproduced by different multi-channel record reproduction systems. FIG. 3 is a block system diagram of one embodiment of the recording system of the record of the present invention, and FIGS. FIG. 3 is a diagram illustrating the frequency spectrum of one example of a signal of an unmeasured channel. 1, 1', f......Harmonic component, 2,? ,7...
...... Cross-modulation component, 3,8,12...Low frequency oscillator, 4゜゛゜"゜Low frequency oscillator, 6,10
...Angle modulator, 9...Mid-high frequency oscillator.

Claims (1)

【特許請求の範囲】[Claims] １ 低域周波数（５０〜２００Ｈｚ程度）の１又は２以
上の第１の単一周波数信号と、中域周波数（５００Ｈｚ
〜３ｋＨｚ程度）で、かつ、該第１の単一周波数信号と
は倍数関係にない周波数に選定された１又は２以上の第
２の単一周波数信号との重畳信号で、所定周波数の搬送
波を角度変調して得た、マルチチャンネルレコード再生
系の被角度変調波帯域内の周波数帯域を占有する第１の
被角度変調波信号、又は該第１の被角度変調波信号と上
記低域周波数で、かつ、該第１の単一周波数信号とは異
なる一の信号との多重信号を被測定チャンネルの信号と
して１本の音溝の片方の壁に記録され、かつ、該音溝の
他方の壁には、該中域周波数よりも周波数が高い中高域
周波数で、かつ、該第１及び第２の単一周波数信号とは
夫々倍数関係にない周波数に選定された１又は２以上の
第３の単一周波数信号で上記所定周波数の搬送波を角度
変調して得た第２の被角度変調波信号と上記低域周波数
で、かつ、該第３の単一周波数信号とは異なる一の信号
との多重信号、又は無変調搬送波が記録されたレコード
であつて、マルチチャンネルレコード再生系にて再生さ
れその再生信号の歪を測定するために用いられることを
特徴とするマルチチャンネルレコード再生系の歪測用レ
コード。1 One or more first single frequency signals with a low frequency (approximately 50 to 200 Hz) and a first single frequency signal with a middle frequency (about 500 Hz)
A carrier wave of a predetermined frequency is a superimposed signal with one or more second single frequency signals selected to have a frequency of about 3 kHz) and not in a multiple relationship with the first single frequency signal. A first angle-modulated wave signal obtained by angle modulation and which occupies a frequency band within the angle-modulated wave band of a multi-channel record playback system, or the first angle-modulated wave signal and the above-mentioned low frequency. , and a multiplexed signal with a signal different from the first single frequency signal is recorded as a signal of the measured channel on one wall of one sound groove, and the other wall of the sound groove , one or more third signals are selected to have a mid-high frequency that is higher in frequency than the mid-range frequency, and are not in a multiple relationship with the first and second single frequency signals, respectively. A second angle modulated wave signal obtained by angle modulating the carrier wave of the predetermined frequency with a single frequency signal and a signal having the low frequency and different from the third single frequency signal. Distortion measurement of a multi-channel record playback system, characterized in that the record is a record on which a multiplexed signal or an unmodulated carrier wave is recorded, and is used to measure the distortion of the playback signal that is played back by the multi-channel record playback system. record for.