Hi everyone,
Many music recordings are normalized such that the largest samples are full-scale, but after interpolation, the signal then usually has to exceed full scale. This often makes digital interpolation filters go into hard clipping, as they are rarely designed to handle this. The recording itself is not clipped, but it makes an interpolation filter without headroom clip. Benchmark Media has dubbed this intersample overs, and found that some recordings have hundreds of intersample overs, see https://benchmarkmedia.com/blogs/application_notes/intersample-overs-in-cd-recordings
When you use a digital volume control, it depends on the exact implementation whether it solves the issue. If the volume control is done before any digital filter and if it is set a few decibels or more below maximum volume, then there is no problem. If the signal first passes through an interpolation filter with no headroom and then through the volume control, reducing volume won't help.
At the end of a now-closed thread, @jean-paul asked me to compile a list of DACs with and without intersample overshoot issues. Unfortunately it will be a very short list, because I have no information about most of them.
Some four years ago, I made a test signal that makes it very easy to determine whether a DAC has or hasn't headroom for intersample overs. It consists of two high-pitched sine waves that produce very audible intermodulation products in a DAC that clips on intersample overs. The test signal and an explanation (in English and Dutch) can be found in the attached zip file. There are two other audio files, depending on whether there is an issue, the test file will either sound like one or the other.
Could everyone who wants to participate play the test signal over their DAC with the digital volume control at maximum and a bit lower than maximum, compare the sound to the other two files and report the result and the DAC or DAC chip model? I will then add the results to the list. To prevent blowing up your ears and your tweeters, the volume should not be too high, so don't do the test if there is no way to control the volume on the analogue side.
Thanks in advance,
Marcel
P.S.: when you play it from a computer, you have to make sure somehow that the computer doesn't change the volume and doesn't do any sample rate conversion, otherwise you might be testing your operating system instead of your DAC.
Lists:
DAC or DAC chip model: clips on intersample overs at full digital volume; clips on intersample overs at reduced digital volume setting (if applicable)
Valve DAC of Linear Audio vol. 13: no; no (the only digital gain settings are 0, -6 and -12 dB)
Typical NOS DAC: no; not applicable
AKM AK449x DACs with the exception of AK4495: probably; no
Gustard X16 (ES9068AS): yes; no (-2 dB)
ES9039Q2M (bohrok2610's DAC): yes; no (-1.5 dB)
Sample rate converter model: clips on intersample overs at full digital volume; clips on intersample overs at reduced digital volume setting (if applicable)
Foobar2000 with RetroArch (resampling to 176.4 kHz): yes; no (-2 dB)
Texas Instruments SRC4392: yes; probably
It should be noted that sample rate converters that have essentially the same fixed-point number ranges at input and output cannot have 0 dB gain without intersample over problems, at least not when they are interpolating.
Many music recordings are normalized such that the largest samples are full-scale, but after interpolation, the signal then usually has to exceed full scale. This often makes digital interpolation filters go into hard clipping, as they are rarely designed to handle this. The recording itself is not clipped, but it makes an interpolation filter without headroom clip. Benchmark Media has dubbed this intersample overs, and found that some recordings have hundreds of intersample overs, see https://benchmarkmedia.com/blogs/application_notes/intersample-overs-in-cd-recordings
When you use a digital volume control, it depends on the exact implementation whether it solves the issue. If the volume control is done before any digital filter and if it is set a few decibels or more below maximum volume, then there is no problem. If the signal first passes through an interpolation filter with no headroom and then through the volume control, reducing volume won't help.
At the end of a now-closed thread, @jean-paul asked me to compile a list of DACs with and without intersample overshoot issues. Unfortunately it will be a very short list, because I have no information about most of them.
Some four years ago, I made a test signal that makes it very easy to determine whether a DAC has or hasn't headroom for intersample overs. It consists of two high-pitched sine waves that produce very audible intermodulation products in a DAC that clips on intersample overs. The test signal and an explanation (in English and Dutch) can be found in the attached zip file. There are two other audio files, depending on whether there is an issue, the test file will either sound like one or the other.
Could everyone who wants to participate play the test signal over their DAC with the digital volume control at maximum and a bit lower than maximum, compare the sound to the other two files and report the result and the DAC or DAC chip model? I will then add the results to the list. To prevent blowing up your ears and your tweeters, the volume should not be too high, so don't do the test if there is no way to control the volume on the analogue side.
Thanks in advance,
Marcel
P.S.: when you play it from a computer, you have to make sure somehow that the computer doesn't change the volume and doesn't do any sample rate conversion, otherwise you might be testing your operating system instead of your DAC.
Lists:
DAC or DAC chip model: clips on intersample overs at full digital volume; clips on intersample overs at reduced digital volume setting (if applicable)
Valve DAC of Linear Audio vol. 13: no; no (the only digital gain settings are 0, -6 and -12 dB)
Typical NOS DAC: no; not applicable
AKM AK449x DACs with the exception of AK4495: probably; no
Gustard X16 (ES9068AS): yes; no (-2 dB)
ES9039Q2M (bohrok2610's DAC): yes; no (-1.5 dB)
Sample rate converter model: clips on intersample overs at full digital volume; clips on intersample overs at reduced digital volume setting (if applicable)
Foobar2000 with RetroArch (resampling to 176.4 kHz): yes; no (-2 dB)
Texas Instruments SRC4392: yes; probably
It should be noted that sample rate converters that have essentially the same fixed-point number ranges at input and output cannot have 0 dB gain without intersample over problems, at least not when they are interpolating.
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