Les Grandes Orgues Cavaillé-Coll

In 1881, Louis Vierne ( a boy of 11 years old) visited for the first time the mass at Sainte Clotilde and heard Cesar Franck play:
I clearly remember that Mass. We arrived early and I waited impatienty. The organ played a mysterious prelude, quite unlike any I had heard at Lille; I was bowled over and became almost ecstatic. There was more to come at the Offertoire, where the master had more time; the theme so unfamiliar, yet so attractive, such rich harmonies, such subtle figurations, and a pervasive intensity that astounded me. I reveled in such delights and wished they would never end. We listened to the Sortie right up to the last note; it was a long paraphrase on the "Ite missa est," full of lyrical flights of fancy that conjured up for me heavenly visions of processions of angels chanting ‘Hosanna’. At the same time, certain melodic progressions and harmonies made me feel uneasy and sensual at the same time. I could not hold back my tears. I knew nothing; I understood nothing; but my natural instinct was violently shaken by this expressive music echoing through my every pore. Faint premonitions of the true meaning of music arose in me. I could not express it in precise terms, but when my uncle asked me what I had felt and what it had done to me, I replied ’it's beautiful because it is beautiful; I don't know why, but it is so beautiful that I would like to play such music and die immediately afterwards’. My aunt was alarmed at my reaction and took me home in a carriage, my legs refusing to carry me. She discussed the matter with her husband and expressed concern. Wisely he reassured her, convincing her that, almost inevitably, this reaction proved my future lay in music.
Louis Vierne, Journal (excerpts), Cahiers et Mémoires de l’Orgue, No. 135bis (Paris: Les Amis de l'Orgue, 1970) 129 (English translation found in : Louis Vierne- organist of Notre Deame cathedral. Rollin Smith, Pendragon Press Hillsdale, N.Y. 1999).

Maurice Duruflé
What more ideal sonority can one desire than that of the full Swell Organ to bring to life a musical thought which had been inspired by just this very sound? The composition of this manual was limited to ten stops, but it was of an exceptional balance: Bourdon 8, Flûte Traversière 8, Gambe 8, Voix Céleste 8, Voix Humaine 8, Flûte Octaviante 4, Octavin 2, Trompette 8, Clarion 4, Hautbois 8. The quality of this Swell Organ was marvelous. Without doubt, a number of technical reasons contributed to this: the size of the Swell box, the responsiveness of the shutters, the placement of the box at the very rear of the organ case, the large sonorous space surrounding the box on all sides giving it an extraordinary resonance, the acoustics of the church and, above all, the genius of the organ builder. All these factors produced a miracle. Add to this the beauty of the 16′ and 8′ foundation stops of the other keyboards. When these stops were combined with the Tutti of the Swell Organ, a registration often indicated by Franck [and Tournemire], the Swell Organ sonority projected astoundingly well. Due to the excellent responsiveness of the Swell shutters, sometimes the full Swell sonority surged to the forefront, sometimes it ebbed, allowing the 16′ and 8′ stops to predominate.
Maurice Duruflé: Mes souvenirs sur Tournemire et Vierne L'Orgue 162: 4, 18

André Fleury
The sound of the foundations with the 8-4 reeds of the Récit was unique. No other organ sounded like that. At Sainte-Clotilde, you could draw anything and it would always sound beautiful. That sound of the 16-8-4 coupled with the 8-4 reeds in the distance was a kind of gentle rustling, simply extraordinary. Just a little touch. Then there was that swell box, so sensitive. It was incredibly effective. When it was shut, you could barely hear a thing, and when it was opened, it suddenly made its presence known… Sainte Clotilde was the most - ‘interesting’ is too dull a word - the most thrilling organ I have ever played.
Interview in La Flûte Harmonique nr 63-64 (1992), pg 7

André Marchal
In 1912, the date at which Ch. Tournemire invited me to touch it for the first time, this organ had had maintenance only once since the death of C. Franck. At the beginning of the century, Mutin added a coupler to the Swell which did not exist yet. This explains that in written passages on the Swell with pedal, Franck doubled the last with the left hand. This organ is considered the most poetic of all the Cavaillé-Coll instruments. It was harmonized by Gabriel Rimburg, being the most artistic of the harmonistes of Cavaillé-Coll. Its sound is characterized by a great poetry of the foundation stops and an extreme lightness of the reeds. The great organ has a composition similar to that of many other organs of that time, only the lack of a Cornet and the clarity of the Mixture of VI ranks, brighter than most mixtures of Cavaillé-Coll, is characteristic for this organ.
The pipes of the GO are arranged on each side of the positive, the latter being located in the front. The positive, almost as important as the Great, has a clarinet which tone color and power allowed Franck to use the full closed Swell (funds and reeds) as accompaniment (the Grande Pieèe Symphonique - Andante). The impact of the positive is still improved by its location in the front. Responding to these two, a small Swell of 10 stops is located behind the positive. The poetry of this keyboard was unique: the smoothness of the foundation stops, the mysterious Voix Céleste and Voix Humaine, the clarity of the Haubois and the exceptional light Trompette and Clairon, they all together allowed this keyboard to equilibrate with the other two. The Swell produced an exceptional effect and allowed a pianissimi of such a restrained character that, when mixing the foundations and reeds, the latter disappeared almost completely when the box was closed. This explains why Franck often retained the reeds of the Swell in his registrations: it was sufficient to close the Swell because then all of the foudatinos dominated. This is hardly ever seen in other organs, even those of Cavaillé-Coll, and that is why the registrations of Franck as he wrote them down can almost never be applied literally.
(Source: disk CD Erato tribute to André Marchal 1958/1994)

Nobert Dufourcq
Before the war, you could refer to the organ at Sainte Clotilde as a ‘masterpiece’ with no fear of being mistaken [...]. It is shocking that after the Couperin family organ at Saint-Gervais, the organ at Sainte Clotilde was not in turn listed [as a Monument Historique], as the most valuable example of Cavaillé-Colls work should be. How we love to remember those beautiful foundation stops, that mysterious Récit buried in its box, that delicious Clarinette, those piercing reeds, that fervent and oh so personal Grand-Choeur.
Les amis de l’orgue nr 30-31 (1937), pg 112