An audio decoder (100, 300) configured to determine a reconstructed frame of an audio signal from an access unit of a received data stream; wherein the access unit comprises waveform data and metadata; wherein the waveform data and the metadata are associated with the same reconstructed frame of the audio signal; wherein the audio decoder (100, 300) comprises - a waveform processing path (101, 102, 103, 104, 105) configured to generate a plurality of waveform subband signals from the waveform data; - a metadata processing path (108, 109) configured to generate decoded metadata from the metadata; and - a metadata application and synthesis unit (106, 107) configured to generate the reconstructed frame of the audio signal from the plurality of waveform subband signals and from the decoded metadata; wherein the frame of the audio signal comprises a lowband signal and a highband signal; the plurality of waveform subband signals being indicative of the lowband signal and the metadata being indicative of a spectral envelope of the highband signal; wherein the metadata application and synthesis unit (106, 107) comprises a metadata application unit which is configured to perform high frequency reconstruction using the plurality of waveform subband signals and the decoded metadata; and wherein the waveform processing path (101, 102, 103, 104, 105) comprises a waveform delay unit which is configured to delay the plurality of waveform subband signals, and the metadata processing path (108, 109) comprises a metadata delay unit configured to delay the decoded metadata, the waveform delay unit and the metadata delay unit being configured to time-align the plurality of waveform subband signals and the decoded metadata, and wherein the waveform processing path comprises an analysis unit configured to generate the plurality of waveform subband signals, and the analysis unit is configured to introduce a fixed delay which is independent of the frame length N of the reconstructed frame of the audio signal, wherein the overall delay of the waveform processing path (101, 102, 103, 104, 105) depends on a pre-determined lookahead between metadata and waveform data. - a waveform processing path (101, 102, 103, 104, 105) configured to generate a plurality of waveform subband signals from the waveform data; - a metadata processing path (108, 109) configured to generate decoded metadata from the metadata; and - a metadata application and synthesis unit (106, 107) configured to generate the reconstructed frame of the audio signal from the plurality of waveform subband signals and from the decoded metadata; wherein the frame of the audio signal comprises a lowband signal and a highband signal; the plurality of waveform subband signals being indicative of the lowband signal and the metadata being indicative of a spectral envelope of the highband signal; wherein the metadata application and synthesis unit (106, 107) comprises a metadata application unit which is configured to perform high frequency reconstruction using the plurality of waveform subband signals and the decoded metadata; and wherein the waveform processing path (101, 102, 103, 104, 105) comprises a waveform delay unit which is configured to delay the plurality of waveform subband signals, and the metadata processing path (108, 109) comprises a metadata delay unit configured to delay the decoded metadata, the waveform delay unit and the metadata delay unit being configured to time-align the plurality of waveform subband signals and the decoded metadata, and wherein the waveform processing path comprises an analysis unit configured to generate the plurality of waveform subband signals, and the analysis unit is configured to introduce a fixed delay which is independent of the frame length N of the reconstructed frame of the audio signal, wherein the overall delay of the waveform processing path (101, 102, 103, 104, 105) depends on a pre-determined lookahead between metadata and waveform data. wherein the frame of the audio signal comprises a lowband signal and a highband signal; the plurality of waveform subband signals being indicative of the lowband signal and the metadata being indicative of a spectral envelope of the highband signal; wherein the metadata application and synthesis unit (106, 107) comprises a metadata application unit which is configured to perform high frequency reconstruction using the plurality of waveform subband signals and the decoded metadata; and wherein the waveform processing path (101, 102, 103, 104, 105) comprises a waveform delay unit which is configured to delay the plurality of waveform subband signals, and the metadata processing path (108, 109) comprises a metadata delay unit configured to delay the decoded metadata, the waveform delay unit and the metadata delay unit being configured to time-align the plurality of waveform subband signals and the decoded metadata, and wherein the waveform processing path comprises an analysis unit configured to generate the plurality of waveform subband signals, and the analysis unit is configured to introduce a fixed delay which is independent of the frame length N of the reconstructed frame of the audio signal, wherein the overall delay of the waveform processing path (101, 102, 103, 104, 105) depends on a pre-determined lookahead between metadata and waveform data.