Nothing beats the feeling of forgetting where ''one of us ends and the other begins'' when playing together with the same voice at one piano, twins Christina and Michelle Naughton say.
The sisters are visiting New Zealand for the first time to play with the New Zealand Symphony Orchestra this month.
''Needless to say, we are pumped.''
They will play their favourite composer, Mozart's, Concerto for Two Pianos in Dunedin.
''There is something very special about all of Mozart's music for four hands and two pianos.
''He wrote these pieces to play with his sister, and you can feel the close relationship the two must have had. There is so much room for witty dialogue, character changes and beauty.''
The tour will also reunite the sisters with New Zealand Symphony Orchestra music director Edo de Waart, who has known the pair since they were students.
''The sisters are marvellous musicians, charismatic and wonderfully talented.''
The sisters are also looking forward to spending time with de Waart ''in his new musical home''.
Growing up learning and playing the piano on their own, the pair, who were born in Princeton, New Jersey, discovered the joy of playing together when they were teenagers.
It was while they were training at the Juilliard School and Curtis Institute of Music they began performing as a duo.
''We find playing together almost conversational, and we love how reacting to each other spontaneously in the moment heightens the excitement of a performance.''
Their decision to perform as a duo was not a conscious one, they said.
''I wouldn't say we actually made the decision with our own two minds.
''Very quickly after we started playing together in our teen years, we realised how playing together brought audiences a sense of unity and therefore joy.
''In today's world there are so many things that bring people further apart, so as soon as we felt we could do something to celebrate unity and bringing people closer together, we knew this is what we wanted to do.''
They put their musical talents down to their mother listening to Bach's Goldberg variations ''almost non-stop'' for months before they were born.
The attraction of the piano is it allows musicians to play multiple voices by themselves.
''Now, when we play four hands or two piano, that number doubles! It is like having an orchestra at your fingertips.''
Being twins does provide some advantages - their hands are of similar size, which helps with voicing, and they have sat in on each other's lessons and had the same teachers.
''However, we would be lying to say that being twins made playing together completely natural and easy. In fact, even as twins, playing with the ''same voice'' at times when the music calls for it is still the most difficult thing.''
Some of the greatest challenges of playing together happen to also be the aspects that bring the pair most joy.
''The way in which one has to be exponentially aware of exponentially more things going on, and how these things interact with one another, when playing as a duo.
''Though this at first seemed to be difficult and at times almost exhausting, we now feel that this heightened awareness can organically lead to more spontaneity and freedom in the context of a performance.''
Being sisters and having that close relationship also had its negatives and positives.
''I think it is both easier and more difficult for the exact same reason ... the ease of being so frank with each other. Certainly both of us have grown a lot musically by having a trusted ear who is able to always give feedback, even when it's not what you want to hear. But that's also precisely what makes it so difficult.''
They have learnt they can never predict or control how they are going to feel before a performance.
''It almost would be worrisome to go into a performance without any anxiety at all. So because of that, we don't have any real ritual - even warming up your hands is not always possible, depending on whether there is a piano backstage. So I guess our pre-concert ritual is to 'go with the flow'.''
While there have been many highlights of their careers so far, the first time each played with an orchestra, at the ages of 9 and 10, are particularly special.
''Not only because each of our entire school classes had come out to support us, but this was the first time that we got to experience the joy in making music with others.
'' Music is about life, and is life in so many ways; so perhaps this is why performing music on stage with other musicians is so emotionally and spiritually powerful.''
Asked what their most terrifying experience had been, they said it did not involve a piano or going on stage, but getting stuck in traffic during Oktoberfest in Germany.
''On the ride over, less than 20min before the interview and more than a mile away from where we needed to be, we got stuck in the middle of a big Oktoberfest parade. The driver got frustrated and threw us out of the car and said 'walk'. Stuck in between so many people we could hardly move, with no normal subways running, and with phones that were getting little to no reception to access maps or contacts.''
The pair, who are based in New York, find themselves travelling more and more. This year there are engagements in Brazil, Belgium, Spain and a variety of US venues, as well as New Zealand.
''Especially with the amount of travelling we do now, there are days spent where we can hardly touch a piano at all, and others where we hardly see anything but a keyboard.''
There is also the jet lag, which they have never become used to.
''When we're on stage, somehow you're able to forget. The thing we love most about travelling is seeing how people around the world are truly much more similar than different.''
At each venue they have to adjust to a new piano.
''We've gotten lighter on our feet - it's almost like trying to make a new friend in each city, adjusting to a new piano. And in our case it's like each one of us making a new friend, and then ensuring that the two ''new friends'' work well together.
They believe their joint experiences with music have brought them closer together.
''I think because we share music together, we are actually closer as siblings than we would have been had we not worked together.''
When at home, the pair still listen to ''quite a bit'' of classical music.
''Though perhaps not piano music so much. Living in New York City, there is no shortage of good jazz concerts, which we enjoy as well.''
