Leo's Audio DSP project

Wednesday, February 21, 2007

Feedback on the chorus / AD DSP Tech Support

* I had the Harman Music Group Sound Engineer Brian Zeleniak listen to the first version of the chorus and received suggestions to improve the sound.

* Contacted Analog Devices DSP Tech Support to find out some details about the way the clock signal is fed to the AD1835 codec.

Friday, February 16, 2007

Crude Chorus Implemented

I implemented a single tap chours. The chorus is driven by a 1Hz sine wave. The delay offset is 30ms and chorus depth is 10 or 20 ms. No interpolation between the samples.

I have 2 configurations:

1- Left channel dry, right channel is left channel with chorus: The chorus sounds like somebody is changing the pitch @ 1 Hz. No atrifacts are present. This is a surprise since no interpolation takes place.

2- Both channels are left with chorus: There are clicks and artifacts just as expected as the result of non-interpolation.

I can't explain why the 2 configurations sound different. In theory they should be the same. I will investigate further.

Wednesday, February 14, 2007

First shot at creating the chorus effect

I took a very naive approach to create the chorus and changed the delay tap time on the fly. At this point I'm still getting undistorted audio but I don't have a significant audable effect.

Experimenting freely made me think about the concept of the chorus more. My next step will be to sit down and learn the theory of chorus and implement the effect more deliberately.

There's a barely audable click on the modulated channel.

Friday, February 09, 2007

Digital Delay Implemented

I successfully created a delayed sample of my left channel and played through the right channel. This is done @ 96 kHz and using the internal memmory of the SHARC 21364. This step required circular buffering which is crucial to any delay implementation.

A/D and D/A rate changed to 96 kHz

Fixed the little glitch in the given audio I/O template and changed the A/D and D/A sampling rate to 96 kHz from 48 kHz.

Wednesday, February 07, 2007

SHARC-21364 is now passing audio

Today I resolved the License issue with Analog Devices Tech Support and passed audio through the new board

Samples (24-bit) are now being read in 32-bit registers (hardware register size is adjustable up to 32-bits). This preserves the sign of the samples at the hardware level.

Seperated left and right channels.

Implemented a circular delay line.

Circular delay line counter isn't incrementing. Will debug this to get the delay line working.

Friday, February 02, 2007

New board arrived

My brand new Analog Devices SHARC ADSP-21364 DPS evaluation board got delivered today. http://www.analog.com/en/prod/0,2877,21364%252DHARDWARE,00.html Thanks go to AD sales person Jared Bates.