user7329: I'd like to build a LED lighting for my house. I've made preliminary tests and I've realized that my 12V transformer emits a considerable electric hum at the Arduino's PWM frequency range (PWM signal from Arduino gets amplified by external amplifier powered by the transformer). 
I know, that I can reduce the audible noise if I will drive the PWM at higher frequency, beyond the human ear's audible range.
AFAIK Arduino itself is not able to give me 8-bit PWM at the >20kHz range. Do you know any feasible hardware high frequency PWMs that will work with the Arduino?

user20548: I am not into hardware but the way we handle it was by using a external PWM designed for LEDs and control that, using an Arduino. The LED driver we used was a TLC5940, see TLC5940 16-Channel LED Driver With DOT Correction and Grayscale PWM Control. This one is controllable using the SPI bus. 
There are several libaries implementing the protocol, i.e PaulStoffregen/Tlc5940.
See Playground from Arduino - TLC5940 for more information.

user2881: Just change the timer prescaler to a lower value. 
E.g. timer2 (PWM pins 3 and 11) has the prescaler set to clock/64 and runs at around 500Hz. So changing it to clock/8 will result in 4kHz. (Sorry, no clock/16 available).
TCCR2 &= ~_BV(CS22);//clear CS22 bit
TCCR2 |= _BV(CS21);//set CS21 bit


7329: <p>I'd like to build a LED lighting for my house. I've made preliminary tests and I've realized that my 12V transformer emits a considerable electric hum at the Arduino's PWM frequency range (PWM signal from Arduino gets amplified by external amplifier powered by the transformer). </p>

<p>I know, that I can reduce the audible noise if I will drive the PWM at higher frequency, beyond the human ear's audible range.</p>

<p>AFAIK Arduino itself is not able to give me 8-bit PWM at the >20kHz range. Do you know any feasible hardware high frequency PWMs that will work with the Arduino?</p>
 20548: <p>I am not into hardware but the way we handle it was by using a external PWM designed for LEDs and control that, using an Arduino. The LED driver we used was a TLC5940, see <a href="http://www.ti.com/lit/ds/symlink/tlc5940.pdf" rel="nofollow">TLC5940 16-Channel LED Driver With DOT Correction and Grayscale PWM Control</a>. This one is controllable using the SPI bus. </p>

<p>There are several libaries implementing the protocol, i.e <a href="https://github.com/PaulStoffregen/Tlc5940" rel="nofollow">PaulStoffregen/Tlc5940</a>.</p>

<p>See <a href="http://playground.arduino.cc/Learning/TLC5940" rel="nofollow">Playground from Arduino - TLC5940</a> for more information.</p>
 2881: <p>Just change the timer prescaler to a lower value. </p>

<p>E.g. timer2 (PWM pins 3 and 11) has the prescaler set to clock/64 and runs at around 500Hz. So changing it to clock/8 will result in 4kHz. (Sorry, no clock/16 available).</p>

<pre><code>TCCR2 &amp;= ~_BV(CS22);//clear CS22 bit
TCCR2 |= _BV(CS21);//set CS21 bit
</code></pre>
