Both Kawai and Roland are reputable brands. But Kawai CN37 is a brilliant digital piano. From my experience with some digital pianos, I wasn't able to use a great range of dynamics, but with Kawai CN37, I can somehow control how my dynamics are expressed on the piano, and it's quite comparable to the likes of an upright acoustic piano. I haven't tried Kawai CA17, CA67 and Roland HP603, HP605, so someone else on this platform might be able to contribute your question. How much is Kawai CN37 in local currency?
There are six things you need to consider buying a digital piano:
1. The sound
The digital piano produces sound by playing pre-recorded sounds of acoustic pianos. The method and equipments used to record these tracks affect the quality of the sound. A good digital piano should sound warm and less digital, closely mimicking an acoustic piano. With that said, everyone prefers different sound quality, and it is important to choose a piano that sounds nice to you.
Apart from the general quality of the sound, you should also listen for the articulation and the decay—the start and the end—of the sound. A digital piano with better control over articulation and decay more closely resembles an acoustic piano and thus sounds more natural.
2. The number of keys
A full-sized piano consists of 88 keys. However, some digital pianos come with only 61 or fewer keys. For advanced piano players, a piano with 88 keys is required. Therefore, if you’re a beginner who’s serious about learning the piano, it is advisable for you to get a full-sized piano.
Polyphony refers to the maximum number of sounds that a piano can produce at any time. This means that a piano with 32-note polyphony can produce up to 32 notes at once. Intermediate players should get pianos with at least 64-note polyphony. For advanced pianists, getting a piano with 128-note polyphony or more is desirable.
One question that I frequently hear is this: a full-sized piano has 88 keys, why should there be a piano with 128-note polyphony? This is because the use of the sustain pedal allows the piano to produce many notes at once. If you’re playing a long string of notes while using the sustain pedal, the piano could be producing more than 88 notes at some point.
4. The touch response of the keys
Touch-sensitivity refers to how responsive a piano is when you play a key with different amounts of strength. The keyboard is able to sense the velocity with which you play the key and correspondingly produces a sound of appropriate volume. A touch-sensitive piano gives you better control over the music’s dynamics, which allows you to play more expressively.
5. Weight of the keys
A digital piano can have keys without added weight, semi-weighted keys, or fully-weighted keys. Manufacturers introduce weighted keys to mimic the heaviness of acoustic piano keys. A digital piano with fully-weighted keys is considered the best option, because its keys most closely resemble those of an acoustic piano. It is a good option for pianists who are planning to buy an acoustic piano eventually.
6. Extra features
Other Instrument sounds
A digital piano has the capability to produce sounds of almost any instruments, ranging from a saxophone to a choir. While this isn’t essential, picking a piano with a large number of instrumental tracks will allow you to choose the sound that suits your music best.
Some common learning tools include:
Keys that light up for you to follow
Dual-mode, in which the keyboard splits into two sections so that you
can play in the same octave as your teacher or friend
These features act as learning aids, which are especially useful for beginners. However, not all learning tools are useful. Thus, it is important to find a piano with extra features that suit you. You can read my colleague's article if you want to compare a digital piano to acoustic piano.
All the best for choosing the piano that is most suited for your needs! Feel free to reach out if you have any more questions.