The Magnetophon tape recorder was one of the first recording machines to use magnetic tape in preserving voice and music. At first, early Magnetophons gave disappointing results. One of the first concerts to be recorded on a Magnetophon was Mozart's
39th Symphony played by the
London Philharmonic Orchestra, conducted by
Sir Thomas Beecham, during their 1936 concert tour. The recording was made on an AEG K2 Magnetophon running at 100 cm/s. The tape used was the early black iron oxide
Fe3O4 type. When Beecham and the musicians heard the playback, they were greatly disappointed with the distortion and noise on the recording. Although the original tape is now lost, the recording survived until the 1990s and has been transferred. Some other surviving tapes show a tendency toward
overmodulation. Later in 1939, the Fe3O4 oxide was replaced by the
Fe2O3 type, which gave a significantly better recording quality, so much that the formula became a worldwide standard as
ferro-oxide until the 1970s when
chromium dioxide tapes, yielding superior but above all longer-lasting sound quality, appeared. Adding a
direct-current bias to the record head gave some improvement, but in 1941, Hans Joachim von Braunmühl and Dr.
Walter Weber, both engineers at the German national broadcasting organisation RRG (
Reichs-Rundfunk-Gesellschaft),
accidentally discovered the technique of
high-frequency bias in which the simple addition of a high level (about 10X the maximum audio level) inaudible high-frequency tone resulted in a striking improvement in sound quality by effectively smoothing the magnetization of unused portions of the audio band. The discovery was made when a Magnetophon producing recordings of extraordinary quality was sent 'for repair'. The machine was found to have an oscillating DC bias
amplifier. Magnetic media are inherently non-linear, but
AC bias was the means whereby the magnetisation of the recording tape was made linearly proportional to the electrical signal which represents the audio component. The Magnetophon became a 'high fidelity' recording system because in so many respects, it outperformed
gramophone recording (which was the
78 rpm system of the time). Many speeches, concerts, and operatic performances were recorded. Since many of the recordings survived World War II they were later issued on LPs and compact discs. One of the more remarkable series of recordings took place at the Vienna State Opera House — in Austrian German
Wiener Staatsoper — in 1944, when the German composer
Richard Strauss recorded many of his famous symphonic poems, including
Don Juan, Till Eulenspiegel, and
Also sprach Zarathustra, with the
Vienna Philharmonic Orchestra. AEG engineers made rapid strides in perfecting the system and had practical
stereo recorders by 1943. Until 1945, about 250 stereophonic tape recordings were known to exist, including some Richard Strauss and
Furtwängler. Only three of those recordings are known to still exist. This includes a performance of
Beethoven's
"Emperor" Concerto with pianist
Walter Gieseking and the Berlin Reichssenders Orchestra conducted by
Artur Rother. This remarkable performance was later issued on LP by
Varèse Sarabande. Later in 1993, the Audio Engineering Society (AES) issued a special CD for the 50th birthday of stereo recording. This CD not only includes the "Emperor" Concerto, but the two other stereo recordings known to exist: a Brahms serenade and the last movement of
Bruckner's 8th Symphony conducted by
Herbert von Karajan. Piano Library also issued the Emperor concerto, and Iron Needle issued the Bruckner recordings (catalog IN 1407). ArkivMusic released a CD of the concerto, as well a later recording Gieseking made of Beethoven's first piano concerto with the
Rafael Kubelik and the
Philharmonic Orchestra. Magnetophon recorders were widely used in German radio broadcasts during
World War II, although they were a closely guarded secret at the time. The Allies were aware of the existence of the pre-war Magnetophon recorders, but not of the introduction of high-frequency
bias and PVC-backed tape. Their intelligence experts knew that the Germans had some new form of recording system but they did not know the full details of its construction and operation until working models of the Magnetophon were discovered during the
Allied invasion of Germany during 1944-45. ==Influence and legacy==