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DSP effects on old hi-fi systems
Neuron
post Mar 24 2014, 14:02
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How do DSP effects on old (well, 90s) hi-fi systems work? I have an old Sony stereo I still use ocassionally so that's why I am wondering. Can things like DBFB and EQ DSP cause digital clipping or it operates outside of the digital domain? I know DSP = digital signal processing, but how come then it works with the cassette player too?
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Apesbrain
post Mar 24 2014, 15:07
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"Digital signal processing" means there is a chip(s) on the circuit board that implements these recalculations in the digital domain. It does not mean the processing is only applied to digital sources. ALL sources are passing through this circuitry then to a DAC (they likely are one in the same) before going to the power amp section. Analog inputs, such as your cassette player, first hit an analog-to-digital converter.

Yes, if sufficient amplification (boost) is applied peaks will exceed digital zero. How much you might hear this is not obvious. It's also possible the circuitry has an "apply effects, but prevent digital clipping" governing rule.
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2Bdecided
post Mar 24 2014, 15:32
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A lot of these things weren't digital. You can also have digital control of analogue filters, and I bet the marketing department would call that digital.

Analogue processing gave way to digital processing when it became more cost effective. Both need to be designed with sufficient headroom.

Cheers,
David.

This post has been edited by 2Bdecided: Mar 24 2014, 15:32
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Neuron
post Mar 24 2014, 16:59
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Thanks, it's Sony MHX-NX-3AV. AFAIK those are from cca 1999, so the processing is probably fully digital or am I wrong? And if analog sources get converted to digital first for DSP processing, what is the resolution and the level it is being digitized to?
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DVDdoug
post Mar 24 2014, 18:04
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QUOTE
And if analog sources get converted to digital first for DSP processing, what is the resolution and the level it is being digitized to?
If they don't publish the specs, it's probably impossible to know (unless you can find a schematic or otherwise identify the ADC & DAC).

But, I would assume the audio specs (noise, distortion, and frequency response) are published, and I assume these specs (and the sound) are at least as good as their analog equipment.

This post has been edited by DVDdoug: Mar 24 2014, 18:06
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stephan_g
post Mar 29 2014, 00:18
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DSPs were definitely available in the consumer electronics realm in 1999, as they had already been used in home theater receivers for a few years at this point. Usually a Motorola 56000 series chip. In case of my trusty '97 vintage Onkyo, we've got an AKM AK5340B ADC (18-bit sigma-delta), XC56004FJ50 (24-bit word length, IIRC), and NPC SM5875 DACs (16-bit sigma-delta). The ADC side strikes me as OK, the DAC side is somewhat basic in this case.
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Neuron
post Apr 14 2014, 20:28
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On a side note, what does the Sony DBFB feature actually do? Does it just boost the bass? Because I seem to hear a "brighter" sound upon turning in on, which could mean that it boosts the highs as well and perhaps attenuates the mids? Can anyone who has knowledge of this please elaborate?
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extrabigmehdi
post Apr 14 2014, 20:59
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QUOTE (Neuron @ Apr 14 2014, 20:28) *
On a side note, what does the Sony DBFB feature actually do? Does it just boost the bass? Because I seem to hear a "brighter" sound upon turning in on, which could mean that it boosts the highs as well and perhaps attenuates the mids? Can anyone who has knowledge of this please elaborate?


According to Sony:
The DBFB (Dynamic Bass Feed Back) circuitry reinforce the bass sound at low listening level. The lower the sound level, the more the bass is emphasized.

Source, this pdf:
https://docs.sony.com/release/TAAV501.PDF

This seems a compensation to the way we perceive frequencies at low volume.
If I interpret correctly the equal loudness curves, the lower is the volume, the lower we are sensitive to the bass, so DBFB compensate this.

Equal-loudness curves here:
http://en.wikipedia.org/wiki/Equal-loudness_contour

Now, I must admit that the name "Dynamic Bass Feed Back" is quite stimulating the imagination of "audiophiles".
I got a similar feature on my old JVC hi-fi, and it only have the dumb name of "bass boost", meh.

This post has been edited by extrabigmehdi: Apr 14 2014, 21:05
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pdq
post Apr 14 2014, 21:41
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My stereo back in the '60s had a "loudness switch" that did the same thing (using only analog circuitry, of course). It tied an RC circuit into a tap on the volume pot so that as you turned the volume down, bass wasn't attenuated as much as higher frequencies.
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Neuron
post Apr 14 2014, 21:49
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So it adjusts bass according to volume? If that is true, it cannot really go into digital clipping can it?
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