The frequency, which controls the pitch, is the same. What varies is the wavelength in accordance with the formula $$ \lambda = \frac{v}{f} $$ where $v$ is the speed, $f$ the frequency and $\lambda$ the wavelength. I'd imagine that in thinner air the sound would be quieter, but I'm not sure by how much. The book on sound was written by Rayleigh, but I haven't read it in ages.
To expand on Xcheckr's answer:
The full equation for a single-frequency traveling wave is
$$f(x,t) = A \sin(2\pi ft - \frac{2\pi}{\lambda}x).$$
where $f$ is the frequency, $t$ is time, $\lambda$ is the wavelength, $A$ is the amplitude, and $x$ is position. This is often written as
$$f(x,t) = A \sin(\omega t - kx)$$
with $\omega = 2\pi f$ and $k = \frac{2\pi}{\lambda}$. If you look at a single point in space (hold $x$ constant), you see that the signal oscillates up and down in time. If you freeze time, (hold $t$ constant), you see the signal oscillates up and down as you move along it in space. If you pick a point on the wave and follow it as time goes forward (hold $f$ constant and let $t$ increase), you have to move in the positive $x$ direction to keep up with the point on the wave.
This only describes a wave of a single frequency. In general, anything of the form
$$f(x,t) = w(\omega t - kx),$$
where $w$ is any function, describes a traveling wave.
Sinusoids turn up very often because the vibrating sources of the disturbances that give rise to sound waves are often well-described by
$$\frac{\partial^2 s}{\partial t^2} = -a^2 s.$$
In this case, $s$ is the distance from some equilibrium position and $a$ is some constant. This describes the motion of a mass on a spring, which is a good model for guitar strings, speaker cones, drum membranes, saxophone reeds, vocal cords, and on and on. The general solution to that equation is
$$s(t) = A\cos(a t) + B\sin(a t).$$
In this equation, one can see that $a$ is the frequency $\omega$ in the traveling wave equations by setting $x$ to a constant value (since the source isn't moving (unless you want to consider Doppler effects)).
For objects more complicated than a mass on a spring, there are multiple $a$ values, so that object can vibrate at multiple frequencies at the same time (think harmonics on a guitar). Figuring out the contributions of each of these frequencies is the purpose of a Fourier transform.
Best Answer
The situation you are describing is an example of Fresnel diffraction (or near-field diffraction).
In general, when a wave propagates every point of the wave front can be thought of as its own source of waves traveling in all directions (called Huygens construction). It turns out that neighboring point sources along an infinite straight wave front reinforce the "forward" direction only, but if you put an obstacle in the way you can see this diffraction.
The mathematics needed is simplified when you look at the effect of this diffraction "far away" (far compared to the wavelength of the wave). In the case of sound, a frequency of 55 Hz (low end of the range of sounds you hear) has a wavelength of about 6 m, so on the scale of your drawing diffraction would occur.
This explains why you can hear the thumping bass of a loud car stereo before the car turns the corner, and only make out the song when the car is in sight.
The calculation of relative sound level into the room as drawn is tricky - it involves an integral that is usually evaluated using a graphical technique called the Cornu spiral, and strongly depends on dimensions and frequency. But as a rule of thumb, "high frequencies travel straighter". And "sound barriers" do work (somewhat) to reduce nuisance noise (for example the noise of cars speeding along a highway).
If you want to estimate the attenuation, you will find this link has some helpful equations and graphs.
UPDATE
There is a problem with the link given: it defines the Fresnel number as
$$N = \frac{2d}{\lambda}$$
But has a confusing definition of $d$. To make things work, you need to set the straight line distance from source to receiver to $D$ (not $d$). If you do that, then
$$d = A + B - D$$
and the Fresnel number is
$$N = 2\;\frac{A+B-D}{\lambda}$$