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Old 7th June 2003, 07:34 AM   #61
deandob is offline deandob  Australia
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Location: Brisbane, Australia
Although not conventional, I will be ripping all my CDs to a PC hard disk and using lossless compression (the audiophile virtues of this approach for digital deserves a fresh thread...). It will be easy to upsample to 88.2Khz using this approach.

More conventionally, I would imagine a DSP or even a PIC type device (frequencies are low, a simple interpolation algorithm can be used) between the i2s and the DAC should work (I need to read up more about the i2s spec to understand this further).

I'm wondering if the difference between a non-os DAC and one that uses the approach I suggested above will break the "magic" that non-os brings.

Regards,
Dean
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Old 7th June 2003, 10:07 AM   #62
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: just a thought on non-os filtering...

Koinichiwa,

Quote:
Originally posted by deandob
I've been looking at a non-os DAC for a while now. Looking around on the net has shown:
- There must be something special about non-os given the DIY interest and the great reviews.
Yup.

Quote:
Originally posted by deandob
- >10K measurements for a non-os DAC are poor, although it does not seem to affect the sound from what people are reporting.
The NOSDAC only gives you what is on the CD. It does not add anything. I think the whole argument is centered around the question if that which is added by the digital filter is beneficial or detrimental to the sound.

Quote:
Originally posted by deandob
- The out of audio band artifacts are high and difficult to filter given the 44.1Khz sampling frequency.
Yes, filtering is not easy, but I always argue that if your system cannot handle the energy up to around 40KHz it is deffective. If you combine the natural Sinc rolloff with even a 1st order filter you get quickly into "safe territorry".

Quote:
Originally posted by deandob
- Common concensus seems to be that for os solutions its the digital filter that affects the sound quality.
Yes. It is the DF that "makes" the sound. I find that older, more "primitive" filters such as the SAA7220 sound better than modern types with much "longer" filters who give superior measurements.

Quote:
Originally posted by deandob
What about applying a simple sample rate doubler that ups the effective sample rate to 88.2Khz and use an analog filter? The analog filter will be much easier to implement a cut off above 20Khz if the sampling rate is doubled.
A sample rate doubler is a Digital Filter.

Quote:
Originally posted by deandob
Either a chip with 2x upsampling (althugh no longer a non-os solution!!) or a simple DSP to modify the i2s bitstream would work??
I would think that it should be possible to realise a primitive 3-Tap oversampling filter either in a PIC device or even in "hardware".

Sayonara
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Old 9th June 2003, 09:30 AM   #63
miguel2 is offline miguel2  Portugal
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Finally got the problem. I had a 330K resistor on the output instead of a 330R one . That is why I had to put sooo much gain in it to get anything. Now it is playing ok, but still have to deal with this hiss (not hum) that I hear if the gain is a bit high - I am using a 15K resistor in the feedback, anything higher makes the hiss audible. This hiss is not dependent on the music volume. My guess is that the problem is on the dirty points of the cd PSU I chose to power the TDA1543 - the output pin of a 7805 as + and chassis as ground...

Miguel
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Old 1st July 2003, 09:04 AM   #64
miguel2 is offline miguel2  Portugal
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Hi,

After trying several PSUs on the TDA1543 I still have the same hiss there. The chip has a I2S connection with two pins directly soldered to jumpers on the board and the third I2S pin with a shielded short wire. I am using 1k resistors at the output.
I guess that the hiss (very audible) is not coming from the psu but somewhere else. Any ideas?

Miguel
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Old 1st July 2003, 09:32 AM   #65
Werner is offline Werner  Europe
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Default Re: Re: just a thought on non-os filtering...

Quote:
Originally posted by Kuei Yang Wang

A sample rate doubler is a Digital Filter.
Not necessarily, unless you regard the degenerate case of coefficients [... 0 0 0 1 0 0 0 ...] as a filter.

It is true, however, that in most applications a useful sample rate doubler will contain a digital filter.

Quote:
realise a primitive 3-Tap oversampling filter either in a PIC device or even in "hardware".
Using even none-too-complex FPGAs like Spartans and lower Virtices and the right tools one could implement I2S -in, I2S-out digital filters with around 20 taps in days if one is prepared to live with simple/simplified coefficients.

A 3-tap filter is next to useless as it will have very little suppression above the original fs/2.
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Old 1st July 2003, 11:27 AM   #66
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: Re: Re: just a thought on non-os filtering...

Konnichiwa,

Quote:
Originally posted by Werner

A 3-tap filter is next to useless as it will have very little suppression above the original fs/2.
That's not the point I'm trying to make. The suppresion of images is not the main issue (as various totally filterless non oversampling DAC's show). My main issue is the frequency domain behaviour and minimal smoothing of the waveform above 6.7KHz. A very short digital filter combined with modest analogue filter without peaking should be able to offer a nearly flat frequency domain behaviour with minimal pre- & post ringing.

Sayonara
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Old 1st July 2003, 12:09 PM   #67
Werner is offline Werner  Europe
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A very short DF will start drooping from DC ...
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Old 1st July 2003, 12:10 PM   #68
fedde is offline fedde  Netherlands
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Quote:
Originally posted by Werner
A very short DF will start drooping from DC ...
What do you mean ?

Fedde
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http://www.fedde.nu, gainclone and non-oversampling DAC audio projects and kits...
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Old 1st July 2003, 12:18 PM   #69
Werner is offline Werner  Europe
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That it will be very far from linear through the pass band.
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Old 8th July 2003, 08:16 AM   #70
Lucas_G is offline Lucas_G  Netherlands
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Elso Kwak wrote in post 58 of this thread:

"I had the opportunity to compare my DAC with the most expensive JK-Acoustics DAC in 't Harde.
http://www.jkacoustics.nl/DACReference.htm
Johan Ketelaar was quite perplexed that I had such a good sound from a homebrew affair. Last Friday I had on audition in my home a Arcam FMJ CD33 and a Marantz SA-17S1. The Arcam was beter on CD's than the Marantz The Arcam is Euro 2000, the Marantz Euro 2500.
My DAC had more bass but less highs than the Arcam. The Marantz had a anomaly in the bass, just did not have it under control. I decided not to buy either of them, as I preferred the sound of my own DAC/Philips CD-650. To my ears it sounds more musical more like the real thing. A week ago I attended harpsichord and clavichord concerts here in town. I don't hear the exaggerated highs at the live concert I hear from upsamplers and Hifi-ish sets. Also the volume is not that high as most Hifienthusiasts like to play, in fact volume is quite low. I concur with Kuei. Y.W. that it is all a matter of taste but I like to gauge my ears every now and then, before I loose track on the real sound."

Elso,

What DAC are you referring to?
Can you please post details of your DAC?

I listened recently to the ARCAM CD 23 (dcs Ringdac) of 2000 Euro and the ARCAM CD 82 (Wolfson dacs) of 1000 Euro.
Maybe I liked the CD 82 a bit more. It has slightly less detail, but it has a much firmer soundstage and bass-drive. All in all a very listenable dac.
However, I would prefer to build my own, so therefore I would be very interested in your solution...

Regards,

Lucas.
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