Gina, noise reduction

Mikko Helin MHELIN at
Mon Dec 8 12:53:47 CET 1997

I played little with I2S input of AudioPCI and noticed a maybe
flaw in design. I took the I2S output from EMU8000 synth
on SB-32 (from DAC input pins) to ES1370, and set on the bits
in register that route the I2S to DAC 2 on EAPCI, and it
worked well, the sound was cleaner than on SB-32. Then
I set on the bit that selects I2S input instead of CODEC ADC
for the recording channel, but the resulting recording was quite 
distorted. I found that the fixed sample frequency for DAC 1 
(used for wavetable) is used to "resample" the I2S input, and 
there was no way to sync both to get clean recording. When the
rate was set to 44.1kHz the sound was cleanest, but still
too distorted. The actual recording was synced to word clock on 
I2S input (I found that when I first connected the bit clock
output to word clock input), but the internal buffers were 
updated at the rate of the fixed frequency clock.

It may be possible to use the I2S input if the clocks are
divided from the master clock of DAC 1, I may try this
later, but it seems there are no easy way for s/pdif input.


There are datasheets on Ensoniq's www-sites semiconductors
section. According to them, there's an extra I2S input
which could be used to connect the s/pdif receiver.
I'm going to try it when I found some time, maybe
on next weekend. The software can't switch the i2s
input on, so I have to write some kind of program
to do it. I hope EAPCI driver doesn't virtualize
and restrict the control port access on ES1370.

Replacing ADC with s/pdif is more difficult, as
you need a sample rate converter between ES1370
and s/pdif receiver, ES1370 (the audioPCI controller)
has 22.4345 (?) MHz crystal, which can't be replaced
by CS8412's 256 fs master clock output (11.2xxx Mhz
for 44.1 kHz sample rate (fs)), 512 fs is needed. 
With a PLL it could be possible, I've never used PLL's, 
so I don't know.


Sounds like a bargain - anyone for PCI Soundcard-DIY ?
Does the Ensoniq card support spdif i/o ? 
Would it be possible to replace the ADC on a soundcard with a Crystal
spdif receiver  ?

I believe Maplin have the SSM Hush chips - I hadn't given them much
thought, but 26 db sounds like a very effective system !
Anyone have any experience with these, or know what the best case output
snr is ?
If it can take a signal with noise at about -70db, and lower that to
-96db it would cover a multitude of sins...

Colin f

More information about the Synth-diy mailing list