Learn, learn, learn... Old but Gold
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Digital audio has come a long way. From the introduction of compact disc to today's high resolution media, we have indeed covered lots of bytes, err miles. Bearing this in mind, how does a "vintage" DAC chip of circa 1993 fare in today's high rez media?
Charles Altman from Altman Micro Machines explains what is more important for digital audio is the sampling rate of our media rather than number of bits. Have a read on his page. Don't worry, I'll wait.
Thanks for coming back. So the higher the sampling rate, the better it is for our "signal reconstruction". Hey, that's what a DAC does basically. So how about some real life example? How does Monica's TDA1545A cope with higher sampled material. And thus, I began my experiment. But I hit a snag. Apparently, high resolution test tones are not easily available. 44.1/16 versions abound but not higher rez. Fortunately, you could create your own high rez wave files by using Linear Tech's excellent LTSpice. I also have a bigger problem in that I don't have a media capable of high resolution. For the sake of you dear readers, I have to spend money... [another excuse to buy!] and I bought a John Kenny modified I2S Hiface module.
The signal path is now... Mac Mini -> jkenny I2S Hiface -> I2S Monica. Software is Channel D's Pure Music Player and music library is via iTunes.
Oh yeah, did I mention I built a new I2S Monica as well? Did I mention I had to haul the whole Mac Mini setup to the listening hall?
All this done [phew!], began feeding test tones. Please note that these test tones are created using the described sampling frequency. Note that no software/hardware upsamping nor over sampling is performed at all.
44.1kHz sampled 1kHz sine wave
10kHz sine wave.
16kHz sine wave
As you could see above, 10kHz above, the DAC is struggling to reconstruct the sine waves.
96kHz sampled 1kHz sine wave
10kHz sine wave.
16kHz sine wave
10kHz is still decent but 16kHz is a stretch...
192kHz sampled 1kHz sine wave
10kHz sine wave.
16kHz sine wave
Wow! 16kHz is no problem here!
So what does all this tell me? The problem of digital audio is not in the equipment. It is in the material. We just need higher sampled data to begin with.
If fed high resolution material, our "vintage" DAC chip is far from an old clunker. It is still capable of reconstructing the signals properly.
In other words, Old is Gold. ha ha! |
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Comments
This is the stepped output waveform of NOS, I take it?
So as you increase the sampling rate, the sinewave reconstruction gets less clunky or stepped in shape so it looks more like the original sine wave signal. OK?
Here's my question - does the 16/44.1 sound OK? If so isn't the sinewave being approximately reconstructed by some interpolation that happens at the speaker's voicecoils?
yes, output from nos dac.
yes, as i feed higher sampled sine wave, the dac is able to reconstruct closer to original sine wave.
the 44.1khz sampled signal sound okay but when compared to higher sampled signal, the higher sampled one sounds cleaner. it sounds "better defined".
yes, some interpolation and smoothening happens at the speakers and our ears but the higher sampled signal, once "smoothened", is closer to original signal.
consider a 20khz sine wave.
44.1khz sampled means only 2 points per period. you can't construct a 20khz sine wave.
88.2khz sampled means 4 points per period. better than 44.1 of course.
176khz sampled means 8 points per period. very easy to construct a sine wave.
yeo
without either, a 1khz sine wave looks like a stepped ladder. engineers won't allow this!
if we put in either/both, then we get a nice sine wave. at the expense of sonics.
So, is it your opinion that the issues you mentioned in 16/44.1 NOS playback are more than compensated for by the removal of the oversampling & filter?
he is the first one to go non-oversampling and filterless, back in the mid 90s.
note that for this test, i didn't use any sd card player nor sd card. it's through a mac mini and jkenny's modified i2s m2tech.
the qa550 sd card player could only play 16/44.1 so the above couldn't be done.
the i2s m2tech plus pure music player software allows up to 384khz sampling rate.
so what you are asking is completely different.
yeo
i don't know. as explained, i never tried that.
yeo
DON'T FORGET 99% of all our today Music
it makes me proud and happy, that you have understood and shown, what I wanted to explain on my website.
Cheers,
Charles :)
thanks for reading and you are welcomed!
yeo
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