DirectSound::SetFrequency usage/emulation?

[dethrace-labs]

Hi, I'm reverse engineering a game originally written for DOS/windows (https://github.com/dethrace-labs/dethrace), and have been working on its audio functionality, replacing calls to directsound with calls to miniaudio!

The original game calls SetFrequency (https://docs.microsoft.com/en-us/previous-versions/windows/desktop/mt708937(v=vs.85)) on a directsound buffer to dynamically change the pitch of a cars engine sound, based on the RPM.

I'm currently looking at ma_sound_set_pitch, which I'm not sure is quite the same thing? Do you have any guidance for how to emulate IDirectSoundBuffer::SetFrequency with miniaudio? I'm using the high-level engine API.

// sound_buffer->lpVtbl->SetFrequency(sound_buffer, rate);
ma_sound_set_pitch(pSound, ...?);

Thanks!

[mackron]

The way I understand it, DirectSound uses resampling to achieve the effect which is exactly what miniaudio does with ma_sound_set_pitch(). The difference is the input parameter. miniaudio uses a scale which means a value of 1.0 will set it to the sound's default pitch, whereas a value of 2.0 will double the pitch (will make it higher) and 0.5 will halve it, etc. It looks like DirectSound uses an actual sample rate for it's input so you would need to do a conversion. You can use ma_sound_get_data_format() to retrieve the sound's default rate (just set the unneeded parameters to NULL). That will then give you enough information to set the scale.

Off the top of my head, it would look something like this (untested):

float pitchScale = sampleRateUsedWithDirectSoundSetFrequency / soundBaseSampleRate;

[dethrace-labs]

Thanks - I'd started experimenting with scaling the calculated directsound rate, but my confusion around the difference between sample rates and pitch modifications meant I didn't follow it through correctly. Your calculation matches my guess, and seems to provide the right sound output, thanks a lot!

We provide updates on our twitter feed (https://twitter.com/dethrace_labs), and I'll be tagging #miniaudio to help spread the word ;)

[mackron]

Glad that's working for you.

I was going to say actually that I might even try your project out at some point. I love those types of recreation projects. I have some long term plans to do a drop-in rewrite of Total Annihilation which I've played around with but never completed - should get back into that...