Group notes with different fonts

[Francesco Petrogalli]

Hi,

Is there a way to print the following bar:

```
r2 <a d>4 <g c>
```

so that the lower notes are printed in \tiny fonts, and the upper ones
are printed with \normalfont?

I tried the the approches below but none off them works:

```
r2 <\tiny g \normalsize c>4 <a d> |
r2 \new Voice << {\tiny a4 g} {\normalsize d' c} >> |
```

Any hint?

Thank you,

Francesco