2011年01月08日

フォノイコライザーEQ11  1号機到着 その2

EQ再生曲線を適応させ、初期盤を再生する喜びは、我が国ではすでに20年以上まえから提唱される方が数は少ないながらも存在した。 その頃は、なんとなく違う、そうでしょう違うでしょう、という思い込み半分のところもあり、実際に納得できなかったところが多かった。 僕自身、それほど大きな違いはないと感じており、耳でイコライジングすればいいことじゃないか、と内心思っていた。 それが変わったのは、英国のコレクターの家でイコライザー可変付再生装置で、ALP/33CX/NIXA等を矢継ぎ早に次々と聴かせてくれたからだった。 良質なヴィンテージ再生装置が初期盤再生には必要なこと、それとEQ曲線をおろそかにしては初期盤を聴く意味がほとんどなくなってしまうということだった。 そう思わせるだけの音楽の味わい、ニュアンスや香り、そして気配!! サザンプトンの古風な家での一晩の音楽体験。 EQの違いをはっきり意識させてくれる、適正なる特性を備えたヴィンテージアンプとそれを反応させるプレイヤーとスピーカーで構成されていた再生装置だからこそ、その違いを体感できたと、今になって思う。 
現在ヴィンテージのコントロールアンプが抱える問題は、フォノ入力部特性が精確なまま保たれている個体が少ないという現実。 特性の良いヴィンテージ製品を探すには、とほうもなく多くの時間と費用が必要とされる。 事実、同じアンプを4台も5台もとっかえひっかえするのは、十年前はともかく、オークションにより急激に良い状態のヴィンテージが消えていっている今となっては現実的とはいえないし、状態がよければどんなヴィンテージでも良いというものでもない。 
EQ11を聴いて最初に感じるのはそれぞれのEQ曲線のポジションの精確さだ。 また再生周波数の中点の位置がちゃんとしているということ。 つまりヴィンテージアンプのフォノイコライザーは得てして、周波数帯域バランスが高い方にずれていてキンキンやかましくて聴くに耐えなかったり、低い方にずれていて高音域がもっさりと抜けていたりする。 EQ11はそれに気づかせてくれる。 周波数帯域のモノサシの役目も負っている。 自分の装置の劣化を認めるのは良い気分ではないのはわかるが、お手持ちのアンプのフォノ部のバランスに問題があれば、イコライザー曲線について云々するどころの話しではない。 愛用のコントロールアンプにEQ11を接続して違いが大きな場合、そのままコントロールアンプ自体の補正に大いに役立つはずであり、周波数特性のバランスがちゃんと取れているだけで、音色の妙やハーモニクスの拡がり、ダイナミクスの伸びが現れてくるはず。 また、愛用のアンプが精確に調整された最上質のものだとしても内蔵のフォノ部とEQ11で、高水準の音格で比較試聴ができる能力を備えている。  
またEQ11を製作したBernstrom氏はステレオLPの再生においても、EQ曲線を可変させて聴く可能性を示唆している。 下の記述を参照して欲しい。 80年代はじめ頃まではレコード会社によってはRIAAでは無くAES,CCIRを使用している例が少なからず存在していたという事実、そうなるとこのEQ11も面白くなってくる。 つづく

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Equalization
Due to recording mastering and manufacturing limitations, both high and low frequencies were removed from the first recorded signals by various formulae. With low frequencies, the stylus must swing a long way from side to side, requiring the groove to be wide, taking up more space and limiting the playing time of the record. At high frequencies noise is significant. These problems can be compensated for by using equalization to an agreed standard. This simply means reducing the amplitude at low-frequencies, thus reducing the groove width required, and increasing the amplitude at high frequencies. The playback equipment boosts bass and cuts treble in a complementary way. The result should be that the sound is perceived to be without change, thus more music will fit the record, and noise is reduced.
The agreed standard has been RIAA equalization since 1952, implemented in 1955. Prior to that, especially from 1940, some 100 formulae were used by the record manufacturers.
In 1926 it was disclosed by Joseph P. Maxwell and Henry C. Harrison from Bell Telephone Laboratories that the recording pattern of the Western Electric (W. E.) "rubber line" magnetic disc cutter had a constant velocity characteristic. This meant that as frequency increased in the treble, recording amplitude decreased. Conversely, in the bass as frequency decreased, recording amplitude increased.

Therefore, it was necessary to attenuate the bass frequencies below about 250 Hz, the bass turnover point, in the amplified microphone signal fed to the recording head. Otherwise, bass modulation became excessive and overcutting took place into the next record groove.
When played back electrically with a magnetic pickup having a smooth response in the bass region, a complementary boost in amplitude at the bass turnover point was necessary. G. H. Miller in 1934 reported that when complementary boost at the turnover point was used in radio broadcasts of records, the reproduction was more realistic and many of the musical instruments stood out in their true form.
West in 1930 and later P. G. H. Voight (1940) showed that the early Wente-style condenser microphones contributed to a 4 to 6 dB midrange brilliance or pre-emphasis in the recording chain. This meant that the electrical recording characteristics of W. E. licensees such as Columbia Records and Victor Talking Machine Company in the 1925 era had a higher amplitude in the midrange region. Brilliance such as this compensated for dullness in many early magnetic pickups having drooping midrange and treble response. As a result, this practice was the empirical beginning of using pre-emphasis above 1,000 Hz in 78 rpm and 33⅓ rpm records.

Over the years a variety of record equalization practices emerged and there was no industry standard. For example, in Europe recordings for years required playback with a bass turnover setting of 250–300 Hz and a treble rolloff at 10,000 Hz ranging from 0 to −5 dB or more. In the United States there were more varied practices and a tendency to use higher bass turnover frequencies such as 500 Hz as well as a greater treble rolloff like −8.5 dB and even more to record generally higher modulation levels on the record.

Evidence from the early technical literature concerning electrical recording suggests that it wasn't until the 1942–1949 period that there were serious efforts to standardize recording characteristics within an industry. Heretofore, electrical recording technology from company to company was considered a proprietary art all the way back to the 1925 W. E. licensed method used by Columbia and Victor. For example, what Brunswick-Balke-Collender (Brunswick Corporation) did was different from the practices of Victor.
Broadcasters were faced with having to adapt daily to the varied recording characteristics of many sources: various makers of "home recordings" readily available to the public, European recordings, lateral cut transcriptions, and vertical cut transcriptions.

Efforts were started in 1942 to standardize within the National Association of Broadcasters (NAB), later known as the National Association of Radio and Television Broadcasters (NARTB). The NAB, among other items, issued recording standards in 1949 for laterally and vertically cut records, principally transcriptions. A number of 78 rpm record producers as well as early LP makers also cut their records to the NAB/NARTB lateral standard.
The lateral cut NAB curve was remarkably similar to the NBC Orthacoustic curve which evolved from practices within the National Broadcasting Company since the mid-1930s. Empirically, and not by any formula, it was learned that the bass end of the audio spectrum below 100 Hz could be boosted somewhat to override system hum and turntable rumble noises. Likewise at the treble end beginning at 1,000 Hz, if audio frequencies were boosted by 16 dB at 10,000 Hz the delicate sibilant sounds of speech and high overtones of musical instruments could survive the noise level of cellulose acetate, lacquer/aluminum, and vinyl disc media. When the record was played back using a complementary inverse curve, signal to noise ratio was improved and the programming sounded more life-like.

When the Columbia LP was released in June 1948, the developers subsequently published technical information about the 33⅓ rpm microgroove long playing record. Columbia disclosed a recording characteristic showing that it was like the NAB curve in the treble, but had more bass boost or pre-emphasis below 200 Hz. The authors disclosed electrical network characteristics for the Columbia LP curve. This was the first such curve based on formulae.

In 1951 at the beginning of the post-World War II high fidelity (hi-fi) popularity, the Audio Engineering Society (AES) developed a standard playback curve. This was intended for use by hi-fi amplifier manufacturers. If records were engineered to sound good on hi-fi amplifiers using the AES curve, this would be a worthy goal towards standardization. This curve was defined by the time constants of audio filters and had a bass turnover of 400 Hz and a 10,000 Hz rolloff of −12 dB.

RCA Victor and Columbia were in a "market war" concerning which recorded format was going to win: the Columbia LP versus the RCA Victor 45 rpm disc (released in February 1949). Besides also being a battle of disc size and record speed, there was a technical difference in the recording characteristics. RCA Victor was using "New Orthophonic" whereas Columbia was using the LP curve.

Ultimately, the New Orthophonic curve was disclosed in a publication by R. C. Moyer of RCA Victor in 1953. He traced RCA Victor characteristics back to the W. E. "rubber line" recorder in 1925 up to the early 1950s laying claim to long-held recording practices and reasons for major changes in the intervening years. The RCA Victor New Orthophonic curve was within the tolerances for the NAB/NARTB, Columbia LP, and AES curves. It eventually became the technical predecessor to the RIAA curve.

As the RIAA curve was essentially an American standard, it had little impact outside of the USA until the late 1970s when European recording labels began to adopt the RIAA equalization. It was even later when some Asian recording labels adopted the RIAA standard.

In 1989, many Eastern European recording labels and Russian recording labels such as Melodiya were still using their own CCIR equalization. Hence the RIAA curve only truly become a global standardization not until late the 1980s.

Further, even after officially agreeing to implement the RIAA equalization curve, many recording labels continued to use their own proprietary equalization even well into the 1970s. Columbia is one such prominent example in the USA, as are Decca, Teldec and Deutsche Grammophon (CCIR) in Europe. To further cloud the picture, some labels even saw different equalization curves arise from differently located pressing plants. (compare Philips using AES in Europe)
To further complicate matters, identical equalization curves existed but were named differently by different recording labels. Some small recording labels advertised their special curves which were the same as Columbia/RCA Ortophonic curves.



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