δοκεῖ γοῦν ἡ φιλοσοφία θαυμαστὰς ἡδονὰς ἔχειν καθαρειότητι καὶ τῷ βεβαίῳ, εὔλογον δὲ τοῖς εἰδόσι τῶν ζητούντων ἡδίω τὴν διαγωγὴν εἶναι.
At least, it is thought that philosophy contains pleasures that are astonishing in both purity and stability and it is reasonable to think that life is more pleasant for those who know than for those who are inquiring.It is unusual, it seems to me, for Aristotle to talk about the purity of a pleasure although it is of course a notion very familiar from Plato. Should we say that Aristotle did think that pleasures themselves varied in terms of purity or should we say instead that Aristotle is citing a reputable endoxon (a Platonic thought) that can be thought to support his general view that contemplative activity is the best activity available to humans and will therefore be accompanied by the best pleasure? 
It is not easy to find any other explicit reference to pleasures being more or less (let alone astonishingly) pure in Aristotle. True, he does say that god’s activity will be very pleasant because contemplation is most pleasant and best (Met. 1072b19–26) and there are similar claims in the NE about how pleasant intellectual activity is for us humans (e.g. 1174b20–23). But these do not make the case for the excellence of such pleasures in terms of the purity of the pleasure concerned.
The closest is at NE 1175b36–1176a3 but it is not easy to interpret:
διαφέρει δὲ ἡ ὄψις ἁφῆς καθαρειότητι, καὶ ἀκοὴ καὶ ὄσφρησις γεύσεως· ὁμοίως δὴ διαφέρουσι καὶ αἱ ἡδοναί, καὶ τούτων αἱ περὶ τὴν διάνοιαν, καὶ ἑκάτεραι ἀλλήλων.According to Bonitz’ Index these are the only two occurrences of the noun καθαρειότης in the corpus. And in fact, setting aside related terms such as katharsis, Aristotle appears not to use cognate terms for ‘purity’ much at all.  The first set of distinctions is between different sense modalities. The senses seem to differ in that the distance senses are purer than the contact senses, with perhaps sight as the purest of all.  Direct contact with the object of perception seems to be associated with impurity of some kind. Something then follows about the respective pleasures of the various senses and also about the pleasures of the senses generally compared with the pleasures of thinking. Provided the ‘similarly’ is thought to mean not just that the pleasures differ as the senses do but that they differ in purity as the senses do, then we have here another reference to pleasures differing in terms of purity (perhaps because their specific sense-objects differ in that regard) and the claim that the pleasures of thought are purer than the pleasures of perception.
Sight differs from touch in purity, as do hearing and smell differ from taste. Their pleasures differ similarly; not only do the pleasures of thinking differ from these but so does each from one another.
There are certainly texts that suggest that Aristotle, like Plato, was prepared to distinguish between different objects of perception in terms of their purity. For example, at De Sensu 439b31–440a6  he first claims that there are some colours that are more pleasant to look at than others because their components are in easily expressible ratios to one another. Here he is borrowing a thought from similar notions about pleasant and unpleasant notes and chords in audible harmonies. He then distinguishes between pure and impure colours. The implication is that the pure colours are the most pleasant to look at. And this is a thought that recurs in the NE in the claim that the activity of sight is engaged most fully when we look at a beautiful object (1174b14–20). All the same, the idea of pure pleasures is not something that Aristotle emphasises except when it comes to offering a rousing claim about the astonishingly pleasant nature of philosophy. The principal work is done by distinguishing between different activities in terms of their value and intensity and claims about different pleasures will follow from that.
 See e.g. G. Van Riel, Pleasure and the Good Life: Plato, Aristotle and the Neoplatonists (Leiden, 2000), 70–71. Cf. Broadie’s note ad loc. in S. Broadie and C. Rowe, Aristotle: Nicomachean Ethics. Translation, introduction, and commentary (Oxford, 2002).
 The bee is the ‘purest’ animal (626a24); there is a reference to those who are ‘pure’ in appearance, dress and general conduct at Rhet. 1381b1.
 For the details of the distinctions between the contact senses and the other senses see T. Johansen, Aristotle on the Sense-Organs (Cambridge, 1997), 178–225.
 De sensu 439b31–440a6: τὰ μὲν γὰρ ἐν ἀριθμοῖς εὐλογίστοις χρώματα, καθάπερ ἐκεῖ τὰς συμφωνίας, τὰ ἥδιστα τῶν χρωμάτων εἶναι δοκοῦντα, οἷον τὸ ἁλουργὸν καὶ τὸ φοινικοῦν καὶ ὀλίγ' ἄττα τοιαῦτα (δι' ἥνπερ αἰτίαν καὶ αἱ συμφωνίαι ὀλίγαι), τὰ δὲ μὴ ἐν ἀριθμοῖς τἆλλα χρώματα· ἢ καὶ πάσας τὰς χρόας ἐν ἀριθμοῖς εἶναι, τὰς μὲν τεταγμένας τὰς δὲ ἀτάκτους, καὶ αὐτὰς ταύτας, ὅταν μὴ καθαραὶ ὦσι, διὰ τὸ μὴ ἐν ἀριθμοῖς εἶναι τοιαύτας γίγνεσθαι.