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Topic: ReplayGain - degrade audio quality? (Read 6193 times) previous topic - next topic
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ReplayGain - degrade audio quality?

I was looking around for information abous Linn's Sneaky DS when I came around this thread in the Linn forum Use of Replay Gain.
They say, that the DS does not support replay gain, because at lower volumes RG will degrade audio quality and increase the noise floor.
Is this only a theory or does ReplayGain really affect the sound qualty?

Edit: oops, mistake in topic title: it should be "degrade audio quality"

ReplayGain - degrade audio quality?

Reply #1 –
Minimally. The idea of not implementing RG support because it "degrades audio quality" is a pretty foolish one.

ReplayGain - degrade audio quality?

Reply #2 –
It's a volume/gain control and it can affect quality/noise like any volume control.  The effects are identical to any digital volume control.  The effects of analog volume controls are similar, except they are placed at a different point along the "audio chain".

There are two issues/concepts to consider...  Total noise (or noise floor) and signal-to-noise ratio (SNR).

If you reduce the volume on your preamp, the signal (and combined noise) goes down while any noise generated in the power amp remains constant.  This is a reduction in SNR.

Since RG is usually reducing signal level while the analog noise (and quantization noise) remains constant, you get a reduction is SNR.  In this case, RG isn't "increasing the noise floor", the noise floor is constant, and it only rises if you increase the (analog) volume to compensate for the gain reduction introduced by RG.

If you increase volume, you also increase any noise present with the signal.  If you increase the volume on your preamp, the background hiss increases.  (The overall SNR actually goes down, because the power-amp noise is constant.)

On the few tracks where RG increases volume, quantization noise will be increased along with the signal.  This is a theoretical increase in noise floor, but quantization noise is usually insignificant compared to the analog noise, and the increased signal means an improved SNR.

ReplayGain - degrade audio quality?

Reply #3 –
The reply in that thread is quite strange...
Quote
Replaygain is not supported on any DS software which has been released up to this point in time. There is no technical reason why it could not be added in the future, hence it is a possibility that DS products will support this if it is believed to be a worthwhile feature and/or there is customer demand for it.

The DS internal volume control is in the digital domain, hence there is the usual digital volume control side affects of implementing replaygain, those being increased noise floor and possible data loss when listening at low volumes (dependant on sampling and recording bit-depths)

If the volume control is in the digital domain, then whether it's ReplayGain that reduces the volume, or the user, the overall result will be identical. You will get exactly the same digital bits reaching the DAC either way.

That's assuming they pipe the ReplayGain value into their existing digital volume control, using it as an offset (or scale factor). That's how I would do it.

If they add it as a separate stage, then obviously that's two digital volume controls, each with a re-quantisation stage. This would be more work, for a slightly worse result, but it might be easier to implement in their architecture and with 24-bit processing it hardly matters.

Cheers,
David.

ReplayGain - degrade audio quality?

Reply #4 –
I think the concerns are when ReplayGain has a positive gain value, rather than reducing the volume.
 

ReplayGain - degrade audio quality?

Reply #5 –
Well, there's an easy answer to that... don't apply positive adjustments.

Or drop everything by 6dB (which equates to using an 83dB reference, as originally intended) - that won't leave many positive adjustments. Don't apply the (very) few that remain.


EDIT: read the Linn quote again...
Quote
there is the usual digital volume control side affects of implementing replaygain, those being increased noise floor and possible data loss when listening at low volumes (dependant on sampling and recording bit-depths)
...that post is written by someone who either doesn't understand it, or hasn't thought it through. The sample rate of the source has no impact at all*, and the bit-depth of the source only has an impact if you restrict processing to that bit depth - but any well designed system, especially one with a digital volume control, is going to work at the maximum bit depth of the hardware (e.g. 24-bits) for all processing - so the bit depth of the source is also irrelevant.

Cheers,
David.

* - OK - double the sample rate = reduce the quantisation noise by the equivalent of 1 bit - but really, the response doesn't sound like it's 1/10th that well thought through!